St. Sebastian River — Sebastian, Florida

The St. Sebastian River is the dark, tannin-stained river whose lower banks border Sebastian before it empties into the Indian River Lagoon. The City of Sebastian describes it as a major tributary of the Indian River Lagoon and reports that the city lies along nearly 9 miles of the lower eastern and southern banks of the river. Measured by land, the city occupies approximately 9,000 acres of the 100,000-acre Sebastian River Watershed, so most of the basin lies outside city limits in the agricultural lands and preserves west of Sebastian.

The river's color comes from its setting. As WQCS reported in December 2023, the St. Sebastian River is classified as a blackwater stream, a name that refers to the tannins leached from leaves along its forested banks. The same report lists manatee, alligator, gar and heron rookeries among the wildlife of the river near Sebastian. Florida's manatee protection rule for Indian River County records the river's other names: Sebastian River, San Sebastian River and Sebastian Creek, with the wider water near its mouth known as San Sebastian Bay.

Upstream of Sebastian the river splits into two prongs, and each has a federal stream gauge. The U.S. Geological Survey lists the South Prong St Sebastian River near Sebastian as a tidal stream gauge in Indian River County with a drainage area of 35 square miles. The North Prong Saint Sebastian River near Micco gauge sits in Brevard County and drains 28.5 square miles. USGS notes both are operated in cooperation with the St. Johns River Water Management District (SJRWMD).

The prongs explain why the St. Sebastian River crosses a county line. In a 2014 report on the river's watershed group, Vero News described the St. Sebastian watershed as including northern Indian River County on its South Prong, southern Brevard County via the North Prong, and parts of both counties to the west via the C-54 Canal. On the regulatory map, the Brevard County manatee rule identifies it as South Florida Water Management District Canal 54 and groups it with the North Prong and the North Fork Sebastian River, also known as Sebastian Creek, in a single Sebastian River Area.

The St. Sebastian River has been on regulators' lists for three decades. The City of Sebastian notes that the Indian River Lagoon National Estuary Program (1996) and the Indian River Lagoon SWIM Program run by SJRWMD and the South Florida Water Management District (1994) identified the river as a priority waterbody in need of water quality rehabilitation and protection. According to the city, the two water management districts flagged a principal concern: large inputs of freshwater that change salinity in the receiving waters near Sebastian, along with suspended matter and nutrients that may degrade water quality and affect local seagrass and shellfish.

Much of that water comes from land use. The city states that agricultural lands west of Sebastian account for a major portion of the run-off to the watershed. Inside the city, General Development Corporation designed and built the street and drainage network in the late 1950s for approximately 15,000 single-family home sites, and that network of canals, ditches and swales delivers most of Sebastian's stormwater to the St. Sebastian River. The city says the system, built to 1950s standards, does not provide the storage or treatment that present development standards require, and that grass beds immediately south of the river's mouth have become more fragmented over time.

In May 2019, Vero Beach 32963 reported that the Florida Department of Environmental Protection had declared parts of the St. Sebastian River impaired about six years earlier due to depleted oxygen and high levels of nitrogen and phosphorus, which feed algae blooms. The paper described the river as one of eight tributaries flowing into the Indian River Lagoon, and one that draws far less scrutiny than the St. Lucie River.

Restoration has come from several agencies at once. After the impairment finding, Vero Beach 32963 reported in 2019, FDEP set restoration goals aimed at raising oxygen levels and lowering nutrient loads, and SJRWMD reclaimed marshland, improved wetlands and created ponds to capture and clean stormwater before it reaches the St. Sebastian River or the canals that drain into it, diverting some cleaned water to the St. Johns River. The City of Sebastian, which manages the drainage canals that empty into the river, adopted a master stormwater management plan and built a large stormwater park with ponds and marshes.

The city's own account adds detail. Its Master Stormwater Management Plan is endorsed by SJRWMD and aims to increase on-site retention and infiltration, and the city has installed 9 nutrient-separating baffle boxes with filters at outfall points to reduce nitrogen and phosphorus reaching the lagoon. In 2015, the City of Sebastian received a League of Florida Cities award for environmental stewardship for its water monitoring and testing program.

Land protection works upstream. Indian River County manages the 37.5-acre South Prong Preserve on CR 510 (85th Street), which includes part of the South Prong of the Sebastian River and a floodplain forest of cypress, water hickory and cabbage palm; the county says conserving the tract buffers the river and removes agricultural nutrient sources. In December 2023, WQCS reported that the Indian River Land Trust acquired 36 acres on the west side of the South Prong along the southwestern border of Sebastian, including about 1,600 feet of river frontage between protected areas that line the river between Route 510 and Route 512. Vero News reported in 2014 that the nonprofit Friends of the St. Sebastian River, incorporated in 1989, was largely responsible for removing a dairy farm beside the South Prong that sent nutrient-laden water into the river.

Boat speeds on the river are set by Florida Fish and Wildlife Conservation Commission rule. Under Rule 68C-22.007 for Indian River County, a year-round slow speed zone covers all navigable waters of the St. Sebastian River, including San Sebastian Bay and the South Fork, west and southwest of the centerline of the US 1 Bridge and north of the centerline of the S.R. 512 Bridge. On the Brevard County side, Rule 68C-22.006 defines a Sebastian River Area covering the North Prong of Sebastian River, the North Fork Sebastian River (Sebastian Creek) and part of the C-54 Canal east of its spillway.

The river's upper reaches meet a large state preserve. Florida State Parks describes St. Sebastian River Preserve State Park, at 1000 Buffer Preserve Drive in Fellsmere, as holding over 23 distinct natural communities and over 70 listed species of threatened flora and fauna, with more than 60 miles of multi-use trails. The park lists canoeing, boating and fishing as popular activities on the St. Sebastian River, notes that all launching facilities are outside the preserve, and maintains a Manatee Overlook for viewing manatees, pelicans and herons in the brackish water.