waters may actually decrease biological uptake of trace metals and reduce their toxicity to aquatic biota.

From a perspective of water use, lake acidification has three major effects: loss of fish populations; increased water clarity, caused primarily by loss of colored organic matter (so-called humic material) from the water column; and increased abundance of acid-tolerant, filamentous algae (primarily Mougeotia), huge, unsightly masses of which may cover the bottom in littoral areas. Fish species differ widely in their sensitivity to acidity (Table 4.1). Smallmouth bass are much more sensitive than largemouth bass. Rainbow trout are impacted in the pH range 5.5 to 6.0; brook trout are much less sensitive. Perch survive and reproduce at pH 5, but survival of young-of-the-year perch is strongly affected at pH 4.7 (Brezonik et al., 1991b). Some Florida lakes with a pH as low as 4.5 have apparently healthy fish communities, although fish production is low because acidic lakes tend to be very oligotrophic. In general, fish production is much more closely related to a lake's nutritional status than to its pH. In a given species, adults are more tolerant than immature forms; lack of