Algal blooms, defined as chlorophyll a concentrations greater than 40
mu g l(-1), are common in Lake Okeechobee, Florida. Using logistic reg
ression techniques, we have developed equations that relate limnologic
al variables to algal bloom occurrence in four distinct open-water reg
ions of this large shallow lake: central pelagic, northwest, southwest
, and a transition region between the western and pelagic regions. Win
d velocity and total phosphorus, which are closely related to resuspen
ded material in the central region, are negatively related to algal bl
oom occurrence there. In the transition region, algal bloom occurrence
is positively related to total nitrogen and wind velocity. Algal bloo
m occurrence is strongly and positively related to total nitrogen and
total phosphorus concentrations in the western regions. The logistic r
egression model predicts an algal bloom probability greater than 95 pe
rcent in the northwest region when total phosphorus exceeds 0.10 mg l(
-1) and total nitrogen exceeds 2.5 mg l(-1). In the southwest region t
he model predicts algal bloom probability of 100 percent when total ph
osphorus exceeds 0.10 mg l(-1) and total nitrogen exceeds 2.8 mg l(-1)
. Given 1994 mean total phosphorus concentrations of 0.05 and 0.04 mg
l(-1) in the northwest and southwest regions, respectively, total nitr
ogen would have to remain below 1.32 and 1.43 mg l(-1), respectively,
to keep the algal bloom probability below 10 percent. Because the lake
is heterogenous, such nutrient standards should be considered on an i
n-lake regional basis for Lake Okeechobee.