Biscayne Bay in Miami: Water Quality, Restoration and Fish Kill Reports

Biscayne Bay is the 428-square-mile subtropical estuary on Miami's eastern edge, and nearly all of it carries some state, county or federal protection.

Miami-Dade County describes the bay as cradled by the mainland to the west and barrier islands to the east, holding two state aquatic preserves, a critical wildlife area, a national park and a national marine sanctuary (Miami-Dade County, About Biscayne Bay). The county itself designates Biscayne Bay an aquatic park and conservation area, and says it is enjoyed by nearly 2.8 million residents.

The largest state unit is Biscayne Bay Aquatic Preserve, which runs from the headwaters of the Oleta River south to Card Sound near Key Largo, excludes all waters of Biscayne National Park, and covers 64,607 acres in Miami-Dade and Monroe counties (Florida DEP, Biscayne Bay Aquatic Preserve). When Biscayne National Monument became a national park in 1980, the southern bay was taken out of the state preserves. The park is 95% water and includes the northernmost Florida Keys (National Park Service, Biscayne National Park).

The Miami River mouth is also one of the bay's oldest human places. The Miami Circle, part of a settlement on both shores of the river's outlet to Biscayne Bay, was discovered in 1998, bought by the State of Florida, added to the National Register of Historic Places in 2002 and declared a National Historic Landmark in 2009 (Florida DEP).

Biscayne Bay's water declined because a century of filling, dredging and canal drainage replaced slow freshwater seepage with pulsed, polluted canal discharges that feed algae and kill seagrass.

The county's history of the bay is specific: since 1890, over 20 percent of the North Bay area was filled and replaced by 30 islands and six causeways, and the Miami River and North Bay canals were dredged to improve navigation (Miami-Dade County, About Biscayne Bay). Before drainage, fresh Everglades water mixed with ocean water to keep salinity low along the western shore, which grew mangroves, oysters and seagrass beds.

Today, natural freshwater flows have been replaced by pulsed, point source discharges from dredged canals built for flood protection. More than half of the freshwater the bay receives enters through the northernmost canals, the same area where the most notable seagrass losses have occurred (Miami-Dade County). Hydrological changes, water management practices, upland development and aged infrastructure have contributed to degraded water quality, seagrass die-offs and algal blooms, which the county documents in part through its surface water quality and benthic habitat monitoring. The county's own seagrass figures show how large the losses are: about 93 percent in the Barnes Sound and Manatee Bay basins in the south, about 85 percent along the eastern shoreline near Coral Gables, and about 66 to 89 percent in the basins north of the Rickenbacker Causeway (Miami-Dade County).

The main nutrients are phosphorus and nitrogen, which the county traces to sewage leaks, septic tanks, stormwater runoff, canal discharges and fertilizer overuse (Miami-Dade County, Fish Kills). Groundwater matters too: FDEP notes that groundwater from the porous limestone Biscayne Aquifer discharges into the bay (Florida DEP), and the county's recovery plan calls the aquifer both the sole source of drinking water and a carrier of pollutants to the bay (Miami-Dade County, Recovery Plan).

Miami-Dade County attributes the August 2020 Biscayne Bay fish kill to low tides, calm winds, poor circulation in the northern basin, heat and large stormwater discharges, and it takes fish kill reports at 305-372-6955.

The county fish kill page lists the physical causes together: extremely low tides, low wind velocities, poor circulation in the northern basin, high air and water temperatures, and large stormwater discharges from the drainage canal system after heavy rain (Miami-Dade County, Fish Kills). It adds that the northern part of the bay is vulnerable to nutrient pollution and has lost significant seagrass over the past 8 to 10 years. The same county page dates the triggering rain event to late May 2019 while naming August 2020 for the kill itself, a mismatch on the county's own page, so both years are given here exactly as the county states them.

The Division of Environmental Resources Management (DERM) is the lead agency in a fish kill or algae bloom, and the county keeps certified canal cleaning contractors on call to remove dead fish quickly, because decomposition releases more nutrients and bacteria (Miami-Dade County). Reports go through the county's online environmental complaints form or by phone at 305-372-6955, 24 hours a day, 7 days a week.

DERM's main office is at Overtown Transit Village North, 701 NW 1st Court, Miami, FL 33136, phone 305-372-6789 (Miami-Dade County, Biscayne Bay).

Miami-Dade County's DERM leads Biscayne Bay restoration under a 2020 Task Force plan, advised by a permanent county board, while the state Biscayne Bay Commission and Florida DEP work on the state side.

The Biscayne Bay Task Force was created in 2019 with nine members, sunset in August 2020, and its report was approved by the Board of County Commissioners in October 2020 (Miami-Dade County, Biscayne Bay Recovery Plan). That report sets seven key areas, beginning with water quality, governance and infrastructure, and calls for pollutant load reduction goals, a fertilizer ordinance, sewer repairs under the county's consent decree and updates to Chapter 24 of the county code. The county also hired a Chief Bay Officer (Miami-Dade County).

The Task Force recommended a permanent board, and the county created the Biscayne Bay Watershed Management Advisory Board through Ordinance No. 21-72. It has 21 members, three of them Miami-Dade County Commissioners, serving four-year terms, and it advises the County Commission and the Mayor on bay management, runoff, marine debris and economic matters (Miami-Dade County, Watershed Management Advisory Board). The State of Florida runs its own Biscayne Bay Commission, which uses science to guide funding, restoration and regulatory changes (State of Florida, Biscayne Bay Commission).

Agendas and board packets for the county board are posted on its page, and the state commission posts an agenda and video for each 2026 session, with minutes for most (State of Florida). DERM publishes a yearly Biscayne Bay Report Card on its bay page, with editions from 2021 through 2026 listed (Miami-Dade County, Biscayne Bay).

The rule most Miami households meet is Miami-Dade's fertilizer ordinance, which bans fertilizer containing nitrogen or phosphorus during the rainy season from May 15 through Oct. 31.

The county's bay tips page states the ban and asks residents to compost or bag yard clippings so they do not wash into storm drains, to keep pool backwash, paint and chemicals out of surface water, and to plant native, salt and drought tolerant trees such as buttonwood, black ironwood and orange geiger that need little fertilizer (Miami-Dade County, Biscayne Bay Tips). On the water, the same page asks boaters to keep trash aboard, never discard monofilament line in the bay, and report derelict vessels, abandoned fishing gear and casitas.

The City of Miami's own drainage planning now names the bay. The city is updating its Stormwater Master Plan, and its list of considerations includes water quality, salt water intrusion, sea level rise projections and protection of Biscayne Bay and other natural features (City of Miami, Coastal and Stormwater Infrastructure). The county, for its part, names stormwater runoff and canal discharges among the main sources of the phosphorus and nitrogen behind algae blooms and fish kills (Miami-Dade County, Fish Kills). Its recovery plan estimates that 80% of marine debris comes from land-based sources (Miami-Dade County, Recovery Plan).

The fertilizer window is a timing tip as much as a rule: the ban covers the rainy season, and the county's fish kill page names heavy rain events that send large amounts of stormwater and nutrient-rich canal discharges into the bay as a cause of fish kills, and asks residents to limit pesticide use, particularly during the rainy season (Miami-Dade County).

Florida DEP lists public boat ramps around Biscayne Bay, including Morningside Park and Gerry Curtis Park in Miami, and runs cleanups every April and September at Pelican Harbor Marina.

The aquatic preserve page names boat ramps at Black Point Park, Crandon Park, Gerry Curtis Park, Haulover Beach Park, Homestead Bayfront Park, Legion Memorial Park, Matheson Hammock Park and Morningside Park, and canoe and kayak launches at East Greynolds Park, Oleta River State Park and the Deering Estate (Florida DEP, Biscayne Bay Aquatic Preserve). Many public access points close from sunset to sunrise. FDEP estimates roughly 16 million people visit the aquatic preserve each year.

Volunteer work is organized. In the Adopt-an-Island program, groups adopt spoil islands in the preserve and commit to four cleanups a year, reporting the debris they remove to the preserve office; the International Coastal Cleanup is held every September and the Baynanza marine cleanup every April, both at Pelican Harbor Marina (Florida DEP). Baynanza ends with Biscayne Bay Cleanup Day, when volunteers work dozens of shoreline sites (Miami-Dade County).

Last verified: October 18, 2026, on the Miami-Dade County DERM and Florida DEP aquatic preserve websites.