Lopez Reservoir is a multipurpose impoundment that was filled during a 30-week period following a series of intense storms during the winter 1968-69. The reservoir is used for flood control, water supply, and recreation, including swimming, fishing, and boating. At full pool Lopez Reservoir has a surface area of 974 acres (394 square hectometres), a maximum depth of 145 feet (44.2 metres), and a shoreline of 22 miles (35.4 kilometres).
Nuisance algal blooms have been a frequent occurrence in the reservoir since the first summer after filling (1969). The dominant bloom species was the blue-green alga Anabaena unispora. Cospecies were the diatoms Stephanodiscus astraea and Cyclotella operculata and the green algae Pediastrum duplex and Sphaerocystis schroeteri. During a bloom of A. unispora in May 1972, the total cell count at the lake surface was almost 100,000 cells per millilitre of water.
Lopez Reservoir is thermally stratified from April until November. Dissolved-oxygen stratification closely parallels the thermal stratification. Anoxic conditions begin to develop in mid-May, and by early July all water below a depth of 40 feet (12 metres) is oxygen deficient.
The application of copper sulfate (CuSO4) to reduce algal production has met with little success. Possible application rates and methods of determining application rates based upon water chemistry are presented.