The Environment Agency is investigating pollution which may have killed a rare dragonfly colony.
The agency found the insects' population suffered significant damage on the upper reaches of the river Arun in West Sussex.
A pesticide killed fish and wiped out invertebrates on a tributary and a 10km stretch of the main river near Horsham.
The agency said it had installed sandbags and pumps to contain the pollution and was investigating the cause of the spill.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article