Algae Blooms and Seagrass Loss
Last update: June 9, 2025
This page will be updated as new information becomes available.
Thousands of acres of seagrass in Florida have died because of nutrient pollution that has caused algae blooms and left manatees without an adequate food source. Learn more about this issue, projects that are being undertaken, and ways you can help.
The Indian River Lagoon (IRL) stretches for 156 miles along Florida’s east central coast. There are more than 4,400 species of plants and animals—including manatees—that are found in the lagoon watershed. Unfortunately, as the direct result of human derelictions over many decades, the Indian River Lagoon has suffered a series of harmful algal blooms, leading to massive losses in seagrass coverage and, in turn, the recent deaths of a heart-rending number of manatees equal to over 25% of the estimated manatee population.
Trouble for Manatees in the Indian River Lagoon
Note: data is preliminary. As of February 6, 2023, there were 800 confirmed carcasses recovered in 2022. Click to view a full-size version of this map.
An excess of nitrogen and phosphorus in waterways can fuel algae and cause it to grow faster than the ecosystem can tolerate. In the IRL, a combination of improperly treated sewage, leaking septic systems, fertilizers, and stormwater runoff has led to eutrophication. This means that frequent harmful algal blooms have blocked the light necessary for photosynthesis. The result: the tragic loss of more than 90% of the seagrass biomass within the Indian River Lagoon.
Before the IRL can be functionally restored, it will be necessary to prevent new sources of nutrient pollution from entering the lagoon as well as strategically removing or sequestering legacy nutrients to make them unavailable as a source of new Harmful Algal Blooms (HAB). Ideally, seagrasses will begin to reestablish on their own, but the process may be facilitated through the restoration of filter feeding organisms and selective pilot seagrass restoration projects. Ultimately, we must reverse those conditions that lead to the loss of seagrasses in the first place if we are going to restore seagrasses.
In 2021, the U.S. Fish and Wildlife Service (FWS) declared an Unusual Mortality Event (UME) for manatees. A UME involves a significant die-off of any marine mammal population and demands immediate response.
Manatees gathering at warm water locations—such as power plants—along the IRL have faced an additional threat, beginning with the 2020-2021 winter season, because there has been very little seagrass or other vegetation for them to eat in the immediate vicinity. Traveling further for forage would mean deadly exposure to cold water, so the manatees ultimately choose to forgo feeding over dying from the cold.
Between December 2020 and December 2022, over 2,000 manatees perished in Florida. 744 of those deaths occurred in Brevard County, which is considered the epicenter of the Unusual Mortality Event.
- See our opinion editorial: A State of Emergency for Manatees in the Indian River Lagoon and Beyond.
- Get more information from the Florida Fish and Wildlife Conservation Commission (FWC) on the Manatee UME.
- Watch Indian River Lagoon: Why All of Us Should Love Seagrass, an informative webinar from the Marine Discovery Center.
- Florida Department of Environmental Protection – Algal Bloom Sampling Status.
- MOTE Marine Laboratory – Beach Conditions Reporting System.
In a healthy ecosystem, free-ranging manatee grazing makes seagrass communities more productive.
Manatees have evolved along with seagrass communities for millions of years and primarily crop the grasses rather than uprooting entire plants, which can actually stimulate the grasses to grow. The loss of seagrass in the IRL is largely due to persistent and recurring environmental events that have changed the ecosystem over time—especially from human sources of pollution.
An Update: 2025
This year, Manatee Appreciation Day brought a hopeful milestone: the official end of the Unusual Mortality Event (UME) that devastated Florida’s East Coast manatee population. The UME, which lasted from December 2020 through April 2022, was the deadliest on record, with 1,255 manatee deaths. Most occurred during the winters of 2020–2021 and 2021–2022, primarily along Florida’s Atlantic coast.
Today, mortality rates have returned to pre-UME levels. Recent health assessments in Brevard County show manatees have improved their physical condition. Increased observations of cow-calf pairs alongside a high rate of perinatal mortality suggest that females are receiving enough nourishment to be able to reproduce again.
While there has been a slight increase in forage in some areas, manatees are far from out of danger. The root causes of seagrass loss must be addressed to sustain even the small gains seen on Florida’s east coast. Statewide, seagrass continues to decline—in places like Biscayne Bay, the Panhandle, parts of Tampa Bay, and the St. Johns River—driven by the same environmental stressors.
Although the UME has officially ended, manatees and their habitat remain under threat. Continued funding for federal and state agencies is essential to support ongoing recovery and protection efforts. Manatees are more than a species in peril—they are a sentinel for ecosystem health. Their survival is directly linked to the quality of the waters we all depend on. Protecting manatees means protecting the future of Florida’s environment—and our own.
What Else Is Being Done to Help Malnourished Manatees?
Save the Manatee Club is a founding member of the Manatee Rescue and Rehabilitation Partnership (MRP), a network of partners who participate in the rescue, rehabilitation, release, and post-release monitoring of sick or injured manatees. We are working together with our partners in the MRP to identify manatees in distress due to devastating seagrass losses in Indian River Lagoon.
Save the Manatee Club and our partners are also working diligently on improving water quality to enable natural regrowth of seagrasses and to replant areas where replanting is feasible now.
If you are at all concerned that a manatee may be sick, injured, entangled, or orphaned, or if you see a manatee that is being harassed or wearing a "tag" or tracking device, please immediately report it to the Florida Fish and Wildlife Conservation Commission (FWC) 24-hour Wildlife Alert Hotline by calling 1-888-404-3922 (FWCC).
What You Can Do
Excessive human-produced nutrient pollution is a growing threat to all seagrass communities. When combined with the warming effects of climate change and sea level rise, these excess nutrients present an even greater danger to the future of seagrasses wherever they are found.
While there are many large-scale sources of pollution, it’s impossible to overstate the value of individual actions. What you do at home can make a big impact—whether you live near the Indian River Lagoon or not. Most people in the United States live in a watershed (a land area that drains to a river, lake, ocean, or other waterway)!
Please don’t feed or give manatees water. Giving food or water to manatees is illegal and teaches them to associate people and/or boats with handouts, which changes their behavior and puts them in harm’s way.
Here are some examples of direct actions you can take to protect our waterways
While Save the Manatee Club works with our partners to strengthen policies that protect water quality, the individual actions of each Florida resident can make a big difference for the health of our waterways. Learn how to do your part and take Save the Manatee Club's pledge to be Fertilizer-Free for Manatees.
- Help reduce pollution and prevent harmful algal blooms from forming.
- Fertilize less, or not at all. Many established landscapes may not need fertilizer. When in doubt, if you must use fertilizer, apply slow-release nitrogen fertilizers to your lawn only once per year. Your local UF-IFAS Extension Office can assist with soil tests, plant recommendations, and specific lawn questions.
- Follow Florida Friendly Landscaping™ principles.
- Know your local fertilizer regulations.
- Take Save the Manatee Club’s Pledge to be Fertilizer-Free.
- Keep yard debris like grass clippings away from stormwater drains.
- Properly maintain your home septic system to ensure it does not leak.
Have your systems inspected every 3-5 years. If you can, consider transferring your home to a city sewer system. - Pick up and properly dispose of your pet’s waste.
- Sign up for cleanups and other events to help protect the manatee’s aquatic habitat. You can find them on the Save the Manatee Club Upcoming Events and Facebook Events. You can sign up to volunteer for future seagrass planting projects here.
- Learn more tips to reduce lagoon pollution:
- Fertilize less, or not at all. Many established landscapes may not need fertilizer. When in doubt, if you must use fertilizer, apply slow-release nitrogen fertilizers to your lawn only once per year. Your local UF-IFAS Extension Office can assist with soil tests, plant recommendations, and specific lawn questions.
More actions you can take for the environment
- Be seagrass safe while you are out on the water.
Prevent damage to seagrasses by avoiding boating over seagrass beds. If you must boat over seagrass beds, trim up your motor and idle to a safe depth before getting on plane, and carefully push your boat away if you run aground. - Send a message to the president and your U.S. senators and representative urging them to come to the aid of manatees and the Indian River Lagoon.
- Send a message to Florida governor Ron DeSantis, asking him to stop the degradation of Florida’s waterways and lead the way in safeguarding the aquatic environment for manatees, other wildlife, and people, too.