>>1881393>This has almost no impact besides fucking up the viewsCheck dams or rock dams that span the width of a stream limits fish movement for certain species during certain settings and depending on time of year. It is harmful to those species in that it makes upstream movement difficult to impossible during low water, thus limiting their habitat. A big enough rock dam can function as a fish barrier stopping movement almost entirely (pic related), which can be either beneficial or harmful depending on the local area. In more arid climates check dams and rock dams are actually very useful in stream restoration and benefit most native warm water species by adding more pools and depth to those pools but still limits fish movement to high water cycles (for a prime example read up on the Turkey Creek restoration project Chiricahua Mountains, Arizona). For colder water species and coastal streams it is usually a detriment and direct impediment on their migration patterns (for a prime example read up on PNW bull trout declines at least in part due to recreational rock dams). Another example from Arizona actually uses check dams as fish barriers in cold trout waters to block invasive trout species movement into native trout habitat (the state has spawning populations of 6 salmonid species but only 2 are native and habitat overlaps).
TL:DR - It generally depends on the area and local ecology, but there are documented cases where rock dams are directly responsible for declines of certain species and beneficial to others.
