river and functions as a salinity barrier. Also, significant flow 
reductions and the inducement of prolonged periods of low or zero flow 
can result in a lack of flushing and exacerbate water quality problems in 
rivers suffering from eutrophication. Thirdly, flow reductions can 
disrupt salinity distributions in the downstream estuary and cause 
salinity changes from dry to wet seasons to be more extreme. The impacts 
of flow reduction in the Hillsborough River may be somewhat lessened by 
the discharge from the Hookers Point Advanced Wastewater Treatment Plant, 
which discharges an average of 51 mgd of tertiary treated effluent near 
the mouth of the river. Any remedial effects of this freshwater source 
are probably spatially variable, particularly in the lower river, but it 
does provide important inflow to Hillsborough Bay in the dry season. 
It should be stated that the Hillsborough, Manatee, and Braden 
River reservoirs were built before there was a great deal of knowledge or 
concern by the public in the region regarding the importance of 
freshwater inflows for the management of estuarine resources. In fact, 
all three reservoirs were constructed before local regulatory agencies 
had rules regarding the withdrawal and use of surface waters. In 1972, 
the Florida Water Resources Act established five Water Management 
Districts who were given the responsibility of regulating the use of 
water resources in their respective regions. When the Southwest Florida 
Water Management District established its rules regarding consumptive use 
in 1975,there was already heavy reliance on these reservoirs for 
municipal water supply. Since the Tampa Bay area is one of the fastest 
growing regions in the country, this reliance has only grown through the 
years. Since the mid-seventies, however, the Southwest Florida Water 
Management District has addressed the issue of freshwater inflow to 
estuaries by sponsoring seminars, workshops, literature reviews and 
several scientific studies. The goal of this involvement has been to 
better evaluate the freshwater inflow needs of regional estuaries so that 
future water resource development can be done in a manner more compatible 
with the management of estuarine resources. 
Instream reservoirs are not the only method of surface water 
storage used for withdrawals in the Tampa Bay area. Just south of the 
Little Manatee River, the Florida Power and Light Corporation operates a 
4,000 acre offstream reservoir which is used for power plant cooling 
water. Water for this reservoir is diverted from the Little Manatee, but 
withdrawals can only be made when the river is over a particular seasonal 
level. Consequently, environmental impacts have been much less than with 
the three impounded streams. Monthly streamflow and withdrawals from the 
Little Manatee during 1979 to 1985 are shown in Figure 9. Pumpage from 
the river generally is highest during mid to late summer, while 
percentage flow reductions are highest during June and July (Table 1). 
30 
