It is not yet known exactly how many fish have died.
Dave Throup, from the Enviornment Agency, said: "We’re dealing with a significant fish kill on a pool near Cannock.
"We’re on site artificially oxygenating the water to try to save as many fish as possible."
Jim Kitchen, from the Environment Agency added: “We are continuing to aerate the fishing pool and to offer advice and guidance to the fisheries owner in order to reduce the environmental impact on site.
"We are also monitoring the local water course to ensure there is no impact further downstream.”