Fish Kill and Algae Bloom in Biscayne Bay

We are passing a tipping point for the Bay not being able to support any life -- literally overnight, the Bay became a deadzone. On Monday morning, August 10th, Miami Waterkeeper’s samplers and members of the public encountered about a dozen dead fish while conducting our weekly fecal indicator bacteria monitoring at Morningside Park. Miami-Dade County DERM monitoring groups conducted their routine monthly sampling nearby, noted very high water temperature (~90 F), and low dissolved oxygen levels. Many species of fish and marine life have been killed, including pufferfish, toadfish, eels, shrimp, trunkfish, pinfish, lizardfish, hogchoker, hogfish, barracuda, parrotfish, angelfish, blue crab, horseshoe crab, seahorses, octopus, lobster, grunts, mangrove snapper and more. 

(Fish kill near Morningside Park, Miami, FL. Source: Kathryn Mikesell)

(Map of community reports of fish kill impacts, updated in real-time. Red dots are fish kill reports; Green dots are algae bloom reports)



The kill seems to have an epicenter near Morningside Park, but dead fish have been seen from North Miami to Virginia Key. We notified the proper agencies and are sending water samples to FWC to check for harmful algae bloom toxins. Many species of fish were killed, including pufferfish, toadfish, eels, shrimp, trunkfish, pinfish, lizardfish, hogchoker, and more. 

On August 12, 2020, Pelican Harbor Seabird Station reported an aggregation of rays nearshore. Scientists believe that this aggregation may be due to low oxygen levels in the water, making it hard for the rays to breathe. Agencies are working on a rapid response to avoid a ray die-off in this area. View the video here

(Photo credit: Christopher Boykin)

On August 15, 2020, Miami Waterkeeper mobilized an emergency aeration effort for Biscayne Bay. In coordination with Miami Dade County and PortMiami, fireboats were sent to oxygen-starved areas of the Bay. Anecdotal evidence seems to suggest that this was an effective temporary measure. Oxygen readings from those areas increased by 30% in the direct vicinity of the fireboats and increased by 15% approximately 100 yards from the boats' aeration areas. In the days that followed, the City of Miami mobilized an emergency aeration response by converting stormwater pumps to help aerate nearshore areas throughout the City, including hot spot locations such as Morningside Park. Anecdotally, these aeration efforts seemed to have been effective as a temporary measure to increase oxygen in these areas. 

(Photo credit: Christy Raynor)

Volunteers and members of our 1,000 Eyes on the Water Rapid Response team quickly rose to scientists' plea for help to remove dead and decaying marine life and organic matter from the water. Decaying marine life produces bacteria which can also consume oxygen from the water column, making even less oxygen available for living marine life. Volunteers removed hundreds of pounds of dead fish from shorelines in dozens of locations in the fish kill impact area. Fertile Earth Worm Farm also mobilized and placed compost bins to collect the dead fish from key locations to assist with removal efforts. 

(Photo credit: Cody Eggenberger)

Conditions appeared to be improving by mid-week. However, by August 20, 2020 residents began to report incidents of strange foam accumulating at the water's surface. This foam was white in nature and also changed color to brown. By August 21, 2020, we began to receive reports of sweeping amounts of foam across Biscayne Bay and by late in the day -- we determined that many areas of the Bay and adjoining canals and waterways were already experiencing algae bloom events. Algae blooms appear to be concentrated in the North Bay area between the Broad Causeway and the 79th Street Causeway. Miami Waterkeeper has been coordinating responses to this algae bloom event with scientists and officials from FIU, UM, NOAA, FDEP, Miami Dade County DERM, City of Miami, North Bay Village, Miami Shores, and the City of Miami Beach. 

(Photo credit: Adam Cohen)

Clean water is what makes Miami, Miami. A dead Biscayne Bay will also affect tourism, fishing, diving, boating, and real estate. People pay a lot of money for beautiful water views. When you have seagrass dying off, when you have sustained fish kills, these are signals of a perishing body of water. It's widespread across northern Biscayne Bay, which means that we're all impacted by this decline. We're finding that we have more and more cases of the Bay not being able to support life.  


Why did this happen?

This fish kill is likely caused by a low dissolved oxygen (DO) event, although we are still investigating. Dissolved Oxygen is the amount of oxygen available for all life in the water, both plants, and animals. DO levels are one of the key indicators of how healthy a body of water is. Low DO levels are a common cause of fish kills, especially in the summer when water is very warm and possibly also polluted. Fish and plants essentially “suffocate” without enough oxygen to breathe in the water.  

Algae blooms can lead to low oxygen conditions, which is why we have been working to stop algae growth and decrease nutrient pollution in Biscayne Bay. These blooms can be caused by too many nutrients like phosphorus and nitrogen in the water. Nutrients such as these can be found in sewage, septic tank effluent, fertilizers, pet waste, and stormwater runoff. 

Biscayne Bay is in a positive feedback loop -- a vicious cycle of decline. Nutrient pollution kills the seagrass and feeds algae overgrowth. Bacteria and algae causes low dissolved oxygen. Low dissolved oxygen kills the fish. The decaying fish and seagrass breed bacteria and more algae. This causes more low dissolved oxygen, creating prime conditions for an algae bloom, and the cycle repeats.

Scientists have been warning about this for years. In August 2019, scientists released a study that reviewed 20 years of data and found that Biscayne Bay is facing a regime change. This means that the bay is changing from a seagrass dominated ecosystem to an algae dominated one. This can be difficult -- if not impossible -- to reverse. We have already seen some initial changes in the Bay including a loss of 21 square miles of seagrass. In some areas, 80-90% of the seagrass has already disappeared. 

Algae blooms happen when there are too many "nutrients" like nitrogen and phosphorus in the water. These nutrients can fuel algae in the water to bloom and can lead to the reduction of water clarity, fish die-offs, human health risks, and the loss of biodiversity.

Scientists believe that land-based sources of pollution are a large contributor to this problem. Such sources include stormwater runoff which contains nutrients from sewage, septic tanks, fertilizer, and other contaminants or chemicals.

Is this normal?

This event is not a “normal occurrence,” but rather a sign that something is seriously out of balance in our Bay. It can be recognized as a “symptom” of high levels of pollution in our water. This fish kill is particularly alarming because of where it occurred. These kills can sometimes happen during the summer in canals that don’t have a lot of water circulation, but to see this over a large area in the open Bay is exceptionally concerning and unusual. 

The types of fish that were killed include those that live at the bottom in the seagrass, which are generally less able to escape poor water quality conditions and those that live in the water column that would typically be able to swim away from poor water conditions. This finding means that the affected area was so big that these water column fish could not escape. 

Algae blooms are not normal. They are a symptom of a larger pollution problem facing Biscayne Bay. 

The area where the seagrass has been dying the most is the same area where the fish kill has been observed, and now where this bloom is now taking place. This is not a coincidence.  This area has many canals drain here, and which pick up the pollution from the land.  This area is highly urbanized and surrounded by septic tanks that leech bacteria and nutrients into the waterways.  Septic tanks must be removed from this area immediately. 

What is Miami Waterkeeper doing to help?

  1. Miami Waterkeeper is processing bacteria samples from Morningside Park, where the fish kill was reported. 
  2. We are collecting citizen reports of dead fish and algae blooms to understand the range of the problem. 
  3. We are organizing scientists and agencies in a response effort.
  4. We are sending water samples to FWC to analyze for harmful algae toxins. 
  5. We are sampling dissolved oxygen levels in the area.
  6. We are keeping the public apprised of new developments related to the severity and extent of this fish kill event.


When you can to do help:

  1. At your community, report any sightings to and sign up to take our 1,000 Eyes training.
  2. At your home, skip the fertilizer over the summer and never fertilize near the water.
  3. Ask your elected officials to fix failing infrastructure that harms the Bay: sewage leaks, septic tanks, and stormwater.
  4. If you see dead birds or unusual bird behavior associated with the fish kill or algae bloom please report it to Miami Waterkeeper.
  5. If you see fish in the water that have cloudy eyes and are washed up on shore, please report it and note it in your email to us.
  6. If you see fish that are gasping for air on the shoreline or are stuck to the bottom on the seagrass and are ‘belly-up,’ please report it.
  7. If you see any usual behavior in marine life, birds, including crustaceans such as shrimp or crabs (i.e. a lot of crabs crawling onto the dock or the beach), please report it.

Please report any of the above to, or through our Instagram @miamiwaterkeeper, Twitter @miamiwaterkeepr, or Facebook.


As an elected official, what can you do to help?

We must restore water quality through limiting nutrient pollution into Biscayne Bay. Here's how:

  1. Stop sewage leaks and fix the sewage system. Read more on our End Sewage Leak campaign HERE.
  2. Retrofit stormwater to store and treat stormwater before it goes into the Bay. 
  3. Remove compromised septic tanks, especially near the water and in low elevation areas.
  4. Enact strict fertilizer ordinances that ban fertilizer use in the summer and near waterways/storm drains. Read more HERE.

Click HERE for a downloadable list of Summarized Policy Action Items to consider as an elected official supporting the current and future health of our Bay.


What can you do to reduce pollution entering our waterways?

Learn more about how to reduce your pollution impact HERE and support our work by becoming a Miami Waterkeeper member HERE

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Fish Kill in Biscayne Bay
Fish Kill and Algae Bloom in Biscayne Bay
HomeMiami Waterkeeper is a South Florida Environmental Group that advocates for Swimmable, Drinkable, Fishable water for all. Working on sea rise, water pollution, coral reef protection, and water issue education.