Indian River Lagoon
Species Inventory

Muck & Nutrients

Black, sticky and smelly, and coating more and more of the bottom of the Indian River Lagoon, the tarry sediments known as muck pose a major threat to the estuary’s function and health.

Photo credit: H. Sweat

While the lagoon’s sediments are mostly made up of sands, silts and shell fragments, an increasing area of the lagoon bottom is becoming covered with a fine-grained, organic-rich mud called muck. Muck accrual in the lagoon has been ongoing for the past 40 to 60 years, mostly as a result of terrestrial and industrial runoff. Although less than 10 percent of the Indian River Lagoon bottom was covered in muck in 1990, coverage continues to grow.

Muck generally settles into depressions in the sediment; in the lagoon, most muck occurs in deeper and dredged areas of the lagoon such as the Intracoastal Waterway as well as at the mouths of most of the lagoon’s major tributaries. Deposits can reach up to 15 feet deep in some areas.

Disturbance from boat traffic, wind and waves can stir up and suspend muck in the water column, clouding the water and reducing available sunlight necessary for healthy aquatic plant growth. Once displaced, muck particles can also be carried with currents and deposited in shallower, nearshore areas such as tidal flats, where it interferes with feeding processes of benthic infaunal and filter feeding organisms. Muck can also settle in salt marshes and mangrove forests, smothering young vegetation.

Credit: M. Bolon

Nutrients and Harmful Wastes

In addition to suspended sediments, storm water runoff (non-point pollution) from urban and agricultural areas can contain high levels of industrial, automotive and household chemicals, fertilizers, pesticides, and animal wastes.

Periodic releases of freshwater from nearby Lake Okeechobee, along with any accumulated wastes and algae, also contribute to water quality issues throughout the Indian River Lagoon estuary.

Streaks of algae bloom on Lake Okeechobee in 2021. Credit: E. Lippisch, J. Thurlow-Lippisch

Although the high bacterial biomass associated with some areas of the lagoon, such as tidal mudflats, can break down these pollutants somewhat, excessive volumes of contaminants can accumulate in the lagoon’s bottom sediments, creating health problems or death for a variety of aquatic organisms.

Excess nitrogen and phosphorous can alter the dominant plant communities of marshes and mangroves. These nutrients can also increase the proliferation of cyanobacterial mats and blooms throughout the lagoon, as well as promote excessive phytoplankton growth that interferes with normal filter feeding processes of many organisms.

An algae bloom proliferates in a marina in Fort Pierce, Florida. Credit: P. Gray


Muck removal dredging projects are a major avenue to address harmful sediments in the Indian River Lagoon. In Brevard County alone, remediation projects aim to remove roughly 6 million cubic yards of sediments that have accumulated over decades. Muck is de-watered and transported elsewhere for storage. A single project in 2019 in the Eau Gallie River removed 600,000 cubic yards of muck, eliminating 1,200 tons of nitrogen and 260 tons of phosphorous from the lagoon.

Reducing new sources of muck is critical to the success of maintaining long-term water quality in the lagoon. To that end, the counties surrounding the Indian River Lagoon, together with the Florida Department of Environmental Protection, the St. Johns River Water Management District and the South Florida Water Management District, are working with communities to:

  • reduce excess fertilizer applications
  • curb stormwater runoff
  • identify and upgrade failing septic systems
  • eliminate wastewater treatment facility discharges
  • restore acres of submerged aquatic vegetation (seagrasses) and oyster reefs