Thousands of fish have died in a pollution spill in the River Sheppey in Somerset.
A 15km (9.3-mile) stretch of the river near Godney is affected, the Environment Agency said.
The agency is working to boost oxygen levels in the water and is spraying the river with hydrogen peroxide.
Samples from the river have been sent for examination and the cause of the pollution is expected to be known later.
In one section of the river there are "at least 3,000 dead fish" - mainly trout and bullheads - but there are also huge numbers of dead invertebrates and insects, an Environment Agency spokesman said.