Harboring a Problem: Investigating Changes in Dissolved Oxygen Levels at King Harbor in Redondo Beach, CA

Part of the Young Naturalist Awards Curriculum Collection.

by Ashley, Grade 8, California - 2015 YNA Winner


intro pic 2
King Harbor at Redondo Beach, California

King Harbor is a beautiful harbor located in the southern portion of the Santa Monica Bay on the Pacific Ocean in my hometown of Redondo Beach, California. Locals and visitors enjoy an average annual temperature of 70º F. to 79º F. in this coastal town, where flip-flops and shorts can be worn year-round. So this seems like paradise, right? Well, not for the millions of sardines that ended up dead in the harbor on March 8, 2011.

I still recall watching the news coverage of the massive fish kill at King Harbor. The news detailed the cleanup to remove 175 tons of dead sardines and the efforts of scientists to uncover the cause. The images from the harbor were shocking, but this was not the first time King Harbor had been in the news for a fish kill. In 2003 and 2005, similar incidents occurred, motivating the city of Redondo Beach to form its own water quality task force and invite researchers to study the coastal waters. Researchers from the University of Southern California (USC) were given permission to set up a high-tech monitoring system in 2006. The monitoring system proved helpful in identifying low dissolved oxygen as the cause of the fish kills.

Dissolved oxygen (DO) is a vital limiting factor in aquatic habitats. In the ocean, higher DO levels are found in the surface layer compared to the bottom layer. Dissolved oxygen is consumed by aquatic animals through respiration and by bacteria during the decomposition of organic materials in the lower layer. DO levels decline when more oxygen is consumed than produced. Because dissolved oxygen enters the water through the air and through photosynthesis, higher DO levels are found in the surface layer. Water movement also increases DO levels because the water becomes aerated. DO levels vary depending on several factors, including season, time of day, temperature, salinity, suspended particle concentrations and water column depth, to name a few.

After reviewing the many factors that impact dissolved oxygen levels, Prof. David Caron at USC concluded, “The fish were jammed in a small space in the harbor and ran out of oxygen.” The fish consumed the dissolved oxygen in the water faster than it could be produced. Basin 1 was described as being hydrodynamically constrained, which I understood as a problem with water circulating in the harbor. Basin 1 was reported to have near-anoxic conditions, while the rest of the harbor had varying levels of hypoxia for more than 10 days after the 2011 fish kill (Stauffer et al. 2012). The researcher’s findings had me asking more questions.

First, what are anoxia and hypoxia? Based on my research, anoxia is defined as a dissolved oxygen level below 0.5 mg/l. Hypoxia is defined as a dissolved oxygen level lower than 2-3 mg/l. At dissolved oxygen levels of 3-4 mg/l, signs of distress may be noted for certain species.

Next, I wanted to know the causes of the hypoxic conditions in King Harbor. Interestingly, I found out that harmful algae blooms and upwelling are two factors that have led to hypoxia in King Harbor in the past. Algae blooms occur when surface water warms in the spring and summer months, particularly when fueled by urban runoff or fertilizers. At first, dissolved oxygen levels increase, but as the algae and phytoplankton die, bacteria on the seafloor use up oxygen to decompose the organic matter. This process lowers dissolved oxygen levels significantly. The USC team ruled out the presence of an algae bloom as a factor in the 2011 event. However, red-tide conditions were present in the 2005 fish kill.

The northwesterly winds that occur between February and October in the Redondo Beach area, resulting in an offshore water movement known as an upwelling, are associated with the 2011 fish kill. These winds blow away the warm surface water, and cold water rises to replace it, changing the balance of DO levels. The upwelling in the Santa Monica Bay brought a large number of Pacific sardines into the harbor, which appeared to cause the 2011 event (Stauffer et al. 2012).

Finally, I wanted to know the impact on King Harbor of being hydrodynamically constrained. I reviewed some of the city’s water-quality task force recommendations for improving harbor circulation and marina aeration. I realized that the semi-enclosed design of King Harbor is problematic because of limited flushing, which impacts oxygen renewal, concentrations of suspended solids, and plankton blooms (Caron 2014). Based on the Environmental Protection Agency’s recommendations for new harbors, preferred harbor designs are built with as few segments as possible, and with an open marina rather than a semi-enclosed design (U.S.E.P.A. 2001).

After reading about ideal marina designs, I became interested in evaluating levels of dissolved oxygen compared to distance from the open ocean. The E.P.A. says, “The ideal situation is one in which the distance between the exchange boundary and the inner portion of the basin is minimized” (E.P.A. 2001). I formed my research question based on a plan of measuring dissolved oxygen levels at increasing distance from the open ocean.


What are the changes in dissolved oxygen levels at King Harbor with increasing distance from the open ocean?


I hypothesize that dissolved oxygen levels will decline with increasing distance from the open ocean in King Harbor because my research explained that water circulation is reduced in semi-enclosed harbors, especially at greater distances from the open ocean.


The independent variable is the distance from the open ocean and the dependent variable is the dissolved oxygen levels. The control is the open ocean (Zone 8). My investigation took place during the same time of day, and the procedures for collecting the data were the same for each testing date within the surface layer. I decided to categorize the 32 testing sites into 8 different zones to understand the general DO levels of the area. I also chose to test each zone four times, on four separate days, to come up with an accurate average.


  • Kayak with oars    
  • Life preserver      
  • Rope
  • White plastic Frisbee
  • 4 metal pipe fittings
  • 10 clothespins
  • Fine-tip Sharpie 
  • Container of freshwater
  • Polaroid Cube camera
  • Waterproof camera case
  • Clipboard
  • Data sheet in plastic page protector
  • Fluval Sea swing-arm hydrometer
  • Fusion Smart Temp thermometer
  • Salifert 02 Oxygen Profi test kit (50 tests)
  • iPhone (timer)
  • Plastic shoe box
  • Laminated map
  • Measuring tape
  • Toothpick


Preparation (before heading to test site)

Identify testing sites with increased distances from the open ocean and make a grid map with individual testing sites in 8 zones for each test date at King Harbor (see Figure 1).

  1. Measure the distance of each testing site to Zone 8, which represents the open ocean, using a 500-feet-to-1 inch scale satellite map (Google Maps). Measure the distances by using the main channels with the most direct route (see Figure 2).
  2. Make four data observation sheets, one for each testing day (see Figure 3).
  3. Make a turbidity tester (a homemade Secchi disk) by cutting a hole through the middle of a Frisbee and feeding the rope through the hole. Next, put the metal pipe fittings on the rope (this is so the plastic Frisbee doesn’t float). Finally, tie a knot at the top and bottom of the Frisbee so the weights stay in place.
  4. Label clothespins with Zones 1-8 (and two just-in-case clothespins), using a Sharpie. 
  5. Next, place the Secchi disk, labeled clothespins, a container of freshwater, and the camera in the waterproof housing, the data sheet in plastic page protector with the clipboard, and the pen, hydrometer, thermometer, dissolved oxygen testing kit, iPhone (timer), and toothpick in the plastic shoe box.
  6. Check outside conditions, using weatherforyou.com, and record on data sheet.
  7. Finally, rent kayak and load testing materials at the same time of day (12:30 to 1 p.m.) on each of the four testing days.

Testing procedures (during investigation at King Harbor)

  1.  Kayak to designated testing site, as indicated on testing grid map.
    The water temperature is measured. (left)The water salinity levels are measured. (right)
  2. Test temperature of water by placing thermometer 10 cm below the water for three minutes and record on data sheet.
  3.  Test salinity by filling hydrometer 10 cm below surface and record on data sheet.
  4. Test dissolved oxygen using a Salifert 02 Oxygen Profi test kit by filling test vial 10 cm below surface. Pour out excess to 5 ml line on vial. Add 5 drops of O2-1 and swirl gently for 20 seconds with toothpick. Add 5 drops of O2-2 and swirl gently for 15 seconds. Set timer for three minutes. Add 5 drops of O2-3 and swirl for five seconds after each drop 
    Ashley collects water to test for dissolved oxygen levels. (left)The test vial is compared to the color scheme to determine dissolved oxygen levels. (right)
    and allow one minute for color to develop. Place the test vial on the white part of laminated color scheme and compare the colors by looking from above. The values on the color chart are in
    mg/l. Record DO amount on data sheet. Once value is recorded, dump contents of collection vial into empty container, rinse the vial first in freshwater and again in ocean water for next testing location.
  5. Test turbidity by lowering the homemade Secchi disk into water until it is not visible from above and mark the spot with a clothespin corresponding to that testing zone. Measure the distance from disk to clips for each zone at home.
  6. Take pictures above and below the surface of the ocean with camera.


A striped sea hare is found in Zone 2. (top left)The oar movement aerates the water in Zone 7. (top right)Zone 7 near the North Breakwater (bottom left)Part of a kelp forest can be seen in Zone 8, the open ocean. (bottom right)

Grid Map

Grid map of King Harbor


Measurements: Distance to Open Ocean

measurements-distance to open
A satellite map was used to find the distance from the open ocean.

Blank Data Sheet

A sheet used for gathering data about dissolved oxygen levels in King Harbor, with entries for water temperature, salinity, dissolved oxygen levels, and other data points.

Table Results from Each Test Date

The columns in blue are the variables, and the other columns are related observations to describe testing conditions. 

table results 1
table results 2
table results 3
table results 4

Graph Results from Each Test Date

dissolved oxygen graph

Photographic Observations from Each Test Date


The kelp at Zone 8 provides dissolved oxygen as a result of photosynthesis. A high amount of sediment in Zone 1 may result in lower dissolved oxygen levels.


The huge waves caused by high surf, aerated the water near Zone 8 but, may have washed nitrates off of the breakwater from bird droppings lowering dissolved oxygen levels. The cloudy day could have also contributed to lower dissolved oxygen levels by reducing photosynthesis. 


Split image. At left: underwater rock formations with a small orange colored fish. At right: A human arm leaning on a railing near water.
Diverse aquatic plant life growing on rocks near zone 7 may increase dissolved oxygen levels through photosynthesis but, surface film in Zone 1 along with near stagnant water conditions may lower dissolved oxygen levels.


In Zone 6 good water clarity allows light to pass through for photosynthesis which increases dissolved oxygen levels but, in Zone 2 the opposite occurs because of surface film blocking sunlight.

Table Results: Averages for Each Zone

table results average for each zone

Graph Results for Average DO Levels vs. Distance for Each Zone

graph results for aveage do levels

Bar Graph Results for Average Dissolved Oxygen Levels for Each Zone

bar graph


The results of the investigation supported my hypothesis. The dissolved oxygen levels were generally lower with increased distance from the open ocean. There was a significant difference between Zone 1 and Zone 8. On average, Zone 1 had dissolved oxygen levels 2.9 mg/l lower than Zone 8. Higher average water temperatures, decreased depths, fewer aquatic plants, decreased water movement, and the presence of surface film were related observations in Zone 1 that may have contributed to lower DO levels. Zone 8 had the lowest turbidity, with visibility up to 27.4 feet, which meant sunlight could reach greater depths to support photosynthesis, as evidenced by my pictures of abundant kelp. Zone 8 also had waves up to nine feet high to aerate the ocean water and increase dissolved oxygen levels.

The use of low-tech devices in my investigation gave me insight into the problems that exist at King Harbor. However, I would expect a higher degree of accuracy from high-tech devices. For example, a DO probe could have given more exact dissolved oxygen levels. One part of my investigation that I could have improved was the salinity readings. Salinity readings for the first three test dates were registering above 37 PPT for most test sites. I later learned that soaking the swing arm of the hydrometer for several minutes would improve its accuracy. I used this method when testing on February 16, 2015 and found that the results seemed more reasonable.


The Redondo Beach King Harbor has proved itself susceptible to massive fish kills due to its low dissolved oxygen levels, problematic harbor shape, and limited flushing. Based on my findings, I am most concerned about low DO levels in Zone 1, which were on average 4.5 mg/l. Slightly below this level, at 4 mg/l, certain species could become stressed and move to a different area. If an algae bloom, upwelling, or an increase of fish in the harbor occurred, the DO levels in Zone 1 could easily become lethal.

The problematic semi-enclosed shape of King Harbor is best illustrated by taking a look at the 5,600-foot-long north breakwater wall that protects the inner harbor. While the breakwater wall adds protection, it also increases the distance water must travel, especially to Basin 1. The harbor also has multiple segments with sharp 90º corners in both Basin 1 and Basin 2. Near-stagnant water conditions were observed in the corners of each basin. In the future I would like to investigate DO levels in harbors with preferred natural shapes, fewer segments, and shorter distances to the open ocean. 

My investigation is relevant for investigating fish kills in other harbors as well. Just last year, Marina del Rey Harbor experienced a six-ton fish kill on May 20, 2014, and Santa Cruz Harbor had a sizable fish kill in July-August 2014 due to hypoxia. Sadly, it is reported that coastal hypoxia is occurring more frequently around the world. Researchers have tied climate changes and increased pollution in coastal waters to this growing problem (Caron 2014).

The Redondo Beach Water Quality Task Force has recognized the need to improve the water quality in the harbor, due in part to repeated “F” grades from Heal the Bay. Because of limited flushing within the harbor, the task force came up with 33 projects, including the installation of aerators. Most of the 33 projects were completed within a year, but to date, aerators are not in place and are awaiting budget approval. I think that the installation of aerators throughout the harbor would be a great solution to the DO problem. Because of my concerns, I will write my City Council a letter explaining the problems I observed in King Harbor and urging them to follow through with harbor circulation improvements.


A very special thanks to…

  • Karen Cordan from Aquatic Fantasy in Redondo Beach
  • Maritza Franco, scientist for the West Basin Municipal Water District
  • Chip, at Rocky Point Kayak Rentals
  • My mom, Andrea, for transporting me to the harbor, paying for supplies and paddling with me.


Barboza, Tony. “Fish Die-Off in Marina del Rey Blamed on Oxygen Depletion.” Los Angeles Times, 20 May 2014. Web. 24 Jan. 2015.

Caron, David. “Biological Considerations for Enclosed Coastal Water Bodies: King Harbor as an Example.” CMANC, Portofino Hotel, Redondo Beach, January 15-17, 2014. Conference presentation. 

City of Redondo Beach Water Task Force. Water Quality Task Force Recommendations Report. 28 June 2006. Web. 1 Feb. 2015. 

Johnson, Pamela. “Nothing Fishy About Sardine Kill.” USC Dormsife, 4 April 2011. Web. 24 Feb. 2015. 

Kemker, Christina. “Dissolved Oxygen.” Fundamentals of Environmental Measurements. Fondriest Environmental, Inc. 19 Nov 2013. Web. 25 Jan 2015.

Kemker, Christina. “Turbidity, Total Suspended Solids and Water Clarity.” Fundamentals of Environmental Measurements. Fondriest Environmental, Inc. 13 June 2014. Web. 25 Jan. 2015.

McDermott, Mark. “Water Task Force Tries to Fix “F” Grades, Part I and II.” Easy Reader, 17 Aug. 2006. Web. 27 Feb. 2015.

Men, Calvin. “Dead Anchovies Inundate Harbor.” Santa Cruz Sentinel, 1 Aug. 2014. Web. 24 Jan. 2015.

“Redondo Beach, Ca.” Google Maps, 24 Jan. 2015. Web. 24 Jan. 2015.

“Redondo Beach (90277)” Weather Forecast and Conditions. Weatherforyou, 1, 7, 13, 16 Feb. 2015. Web. 1, 7, 13, 16 Feb. 2015.

Redondo Beach City Council Minutes. An Adjourned Regular Meeting. 13 Feb. 2010. Web. 1 Feb. 2015.

Stauffer, Beth, et al. “Effects of an Acute Hypoxic Structure in a Coastal Harbor of Southern California.” Estuaries and Coasts, 15 Sept. 2012. Web. 1 Feb. 2015.

U.S. E.P.A. Dissolved Oxygen and Biological Oxygen Demand. U.S. Environmental Protection Agency, Washington, D.C., 13 Mar. 2009. Web. 25 Jan. 2015.

U.S. E.P.A. Marina Flushing Management Measure-II. Siting and Design. U.S. Environmental Protection Agency, Washington, D.C., 2001. Web. 25 Jan. 2015.