Read the pages indicated by Z-24 and study Behavior Objective #36. Now let us consider some fresh water biomes, particularly lakes and ponds. Natural lakes tend to be of recent origin. Geologically speaking, they are most numerous in the glaciated parts of northern America and Eurasia. Lakes also occur in regions of recent volcanism, either in craters of volcanoes or where water was dammed up by lava flows. In addition, they are formed by slifting of rivers, by beaver dams, and by man. Actually, sharp boundaries do not exist between these habitats because erosion and sedimentation are constantly changing them. Upstream, the communities are relatively simple, with fish such as trout that are intolerant of low oxygen and high temperatures and a few invertebrates, algae and mosses that can attach to rocks. Downstream as the water becomes more turbid and pools form, photosynthesis is limited to a narrow upper zone near the banks. Attached algae and cyanobacteria are predominant in shallow areas, and plants can grow near the banks.  Bacteria and fungi become more abundant in the sediments, relying on organic material brought in from upstream. What kind of fish would you expect to find downstream and why?