They cut only a few trees at a time and they replant new trees so the soil won't wash away. Dams can also be a problem to fish because they stop the fish from migrating up stream. But people have built fish ladders so the fish can get up stream. They also raise fish in hatcheries to replace the fish populations that have been lost through dams. Cattle grazing can cause problems, too.
Cattle are a problem when they graze too close to a stream.
They can cause disease in the water and trample vegetation. Fencing cattle away from rivers keeps rivers clean and vegetation growing. Poor fishing practices can be a problem, also. Gill netting can kill more than just fish. Gill netting is now against the law in most areas.