Residents have reported a foul smell off the coast of Worthing and discolouration of a large patch of water.
Worthing and Adur councils are investigating but were unable to confirm the source of the smell or possible spill.
A spokesperson for Worthing and Adur councils said:
“We believe this is just grit and dirt that naturally builds up in surface water pipes, which there is one in this location, during spells of dry and hot weather.
“There is not a sewage pipe in the nearby area. However Southern Water are sending a team to investigate immediately as a precaution.”
Southern Water have been approached for comment and are looking into the situation.