irrigation, in wet periods, agricultural water from the farms could be back-pumped from the drainage canals into the lake. The opening of Beauclair Canal in 1948 permitted better drainage of Lake Apopka to a downstream chain of lakes and lowered the lake level. This alleviated concerns of muck farm owners that future storms would weaken or destroy the dikes and reflood their croplands. In 1946 the lake waters were still clear. However, in the fall of 1947, soon after a severe hurricane had uprooted large quantities of aquatic plants, the first plankton bloom was observed. The dense beds of rooted aquatics were never reestablished, probably because they could not compete with planktonic algae in the nutrient-rich waters.
Clugston (1963) did not discuss the effects of the hurricane but stated that a combination of external factors probably increased the fertility of the lake that led to the first algal bloom in 1947. First, a water hyacinth control program resulted in large amounts of decaying vegetation. Second, a citrus-processing plant at Winter Garden increased its capacity considerably between 1946 and 1950 and its release of waste products. Third, muck farms at the north end of the lake were expanded greatly in the 1940s. Water pumped out of the farming areas may have added nutrients and contributed to siltation in the lake. Fourth, citrus groves located along the eastern and western shores may have contributed nutrients. Finally, a sewage treatment plant at Winter Garden was pumping effluent into the lake.
The game fish population comprised 35 percent of the species present, and gizzard shad made up 20 percent of the total fish population by weight in 1947 when the plankton bloom was first noted (Clugston, 1963). As the plankton bloom persisted, the gizzard shad probably increased greatly in numbers but were small in size, providing excellent forage for game species. As a result, game fish constituted 69 percent of the total population in 1950. From 1947 to 1950 the estimated weight of the total fish population increased tenfold. By 1956-1957, however, the game fish population had dropped to 18 percent of the total. Shad, which made up most of the remaining 82 percent, are thought to have become too large and numerous to be cropped by game species. In an effort to alleviate the shad problem, the Game and Fresh Water Fish Commission treated the lake with rotenone in three successive years; 1957, 1958, and 1959. An estimated 9 million kilograms of gizzard shad were killed with the three treatments. These fish were left in the lake to decompose and release nutrients. In May 1963, 1.4 million kilograms of fish were reported killed by gas (oxygen or nitrogen) embolism (Schneider and Little, 1973).