Streams are the heart of drainage basins and their watersheds. Water that falls to Earth or surfaces from the ground is collected by watersheds and fed into streams. Streams, whether the tiny creek in your neighborhood park or the great Mississippi River, carry life-sustaining water to wildlife, farms, towns and cities. In Florida, thousands of lakes are maintained by a combination of stream flow and groundwater upwellings called springs. Streams also replenish our groundwater. Without natural stream flows, neither our ecology nor economy could survive.
The amount of water moving in a stream is referred to as the discharge or flow. "Discharged" is preferred, as "flow" is often used as a general term when discussing the movement of water (e.g., "Did you see any flow in the creek?"). Factors that affect stream discharge include: drought; thunderstorms; hurricanes; pumping for agricultural, municipal and industrial uses; dams; destruction of watershed and recharge zones by sprawl; and other land use changes. One of the lesser known, but critically important, functions of streams is that they convey great quantities of freshwater to bays and estuaries on both the east and west coasts of Florida. Without these constant deliveries to freshwater, Florida's bays and estuaries — the spawning and nursery grounds for virtually all near-shore fish species, as well as crabs, shrimp, oysters and scallops — would perish, along with it Florida's $140 million dollars/year commercial fishing industry and burgeoning aquaculture business.
In Florida, United States Geological Survey, water management districts, Florida Department of Environmental Protection (FDEP), as well as many counties and municipalities, measure stream discharge. These entities measure stream discharge for a wide variety of purposes such as wastewater permitting, flood control, flood prediction and warning, water resource management and conservation, and wildlife preservation. FDEP established Minimum Flows and Levels (MFL) for Florida's lake and streams in order to prevent significant harm as a result of withdrawals. The water management districts are required by S. 373.042, F.S. to develop a priority list of water bodies for which they will establish MFL. Each year the districts update their list and submit them to FDEP for review and approval. A map showing currently adopted MFLs can be viewed at: https://floridadep.gov/water-policy/water-policy/content/statewide-mfl-map
In addition to reviewing the districts' priority lists each year, FDEP Office of Water Policy also reviews MFL proposals for specific water bodies. The Office actively works with the water management districts to ensure that the proposed MFL is consistent with applicable rules, statutes, and other FDEP guidance.