We're often not allowed to cut grass along ditches because it's deemed as fish habitat, but on some watercourses we are allowed to, and in those courses we don't have to do any actual excavating of ditch material. It can go 10 to 15 years without any real work in those ditches, just by cutting the grass.
The frog benefits from that grass being shorter. If it grows quite tall and falls over in the winter, it's not good habitat for the frog either.