Hillsborough River 
The Hillsborough River, which enters Hillsborough Bay in the 
center of downtown Tampa, comprises the largest and most diverse basin 
draining to Tampa Bay. All totaled, land use in the Hillsborough River 
basin is estimated at 54% agricultural, 14% range, 13% wetlands, and 15% 
urban. 
The drainage basin for the upper Hillsborough River (headwaters to 
Fletcher Avenue) is primarily agricultural, range, or wetlands as the 
small towns of Zephyrhills and Plant City are the only urban centers in 
the basin. At least ten principal tributaries enter the upper river 
including Crystal Springs, which provides baseflow during dry periods. 
Without going into detail, water quality in several of these tributaries 
has been degraded by agricultural runoff and various industrial or 
municipal discharges. The main channel of the upper river, however, is 
in excellent condition, as the floodplain is largely protected under 
public ownership, and no point source discharges occur on its shore. 
Cypress Creek, a major tributary of the Hillsborough, enters the river 
just above the City of Tampa. This creek drains extensive wetlands and 
contributes water to the river that is high in color and relatively low 
in nutrients, BOD, and bacteria. Due to the assimilative capacity of the 
upper river and the influence of Cypress Creek, water quality problems 
observed in various upstream tributaries are largely unapparent 
downstream. Where it flows into the City of Tampa, the Hillsborough 
River has good water quality characterized by high levels of color and 
dissolved organic carbon and relatively low levels of nutrients, 
turbidity, and coliform bacteria (Table 2). 
Once the river reaches Fletcher Avenue it quickly takes on the 
characteristics of an urban river. Seven miles downstream from Fletcher 
Avenue the river is impounded, creating a long, narrow reservoir which is 
surrounded by the cities of Tampa and Temple Terrace. Lands draining to 
this reservoir are approximately 75 percent urban and 25 percent open 
space. Stormwater from this area, however, averages only five percent of 
the net inflow to the reservoir with the remainder supplied by the river 
(Priede-Sedgwick, Inc., 1980). Principal water quality problems in the 
reservoir are high nutrient and metal concentrations, low dissolved 
oxygen in deeper waters, dense growths of water hyacinths and periodic 
blooms of blue green algae. Algal blooms are most common in spring and 
early summer when flows are low, residence time is long, and temperatures 
are increasing (Metcalf and Eddy, Inc., 1983). 
The lower Hillsborough River consists of the 11 mile, tidally- 
affected reach downstream of the dam. The lower river receives 
freshwater inflow from reservoir releases, stormwater runoff, and Sulphur 
Springs, an artesian spring that averages 40.8 cfs discharge. The 
immediate basin for the lower river is approximately 40 square miles in 
size, intensely urban, and primarily drained by storm sewers. Water 
quality in the lower river is controlled by inflow from the reservoir and 
stormwater runoff, but the effects of stormwater vary considerably 
between seasons and among parameters. Coliform bacteria and heavy metals 
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