Bacteria are present in all regions of lentic waters. Lake ecosystems are a prime example of lentic ecosystems. Perlidae are usually lotic and lentic erosional. Logperch are benthic, nonguarding egglayers, whose embryos drift to lentic areas after hatching. "D. magna" is a key species in many lentic habitats. For example, separate standard weight equations have been published for lentic and lotic rainbow trout. These substances dissolve in atmospheric moisture and enter lentic systems as acid rain. For a detailed look at these processes, see lentic ecosystems. Other vertebrate taxa inhabit lentic systems as well. Shallow lentic systems might also fill in as swamps encroach inward from the edges. Freshwater ecosystems can be divided into lentic ecosystems (still water) and lotic ecosystems (flowing water). Lentic systems gain most of their energy from photosynthesis performed by aquatic plants and algae. "Lentic" refers to stationary or relatively still water, from the Latin "lentus", which means sluggish.