Families could only stand and watch as a poisoned bird almost drowned.

A mystery bug in Brooklands Lake, East Worthing, which is believed to flourish in hot temperatures, has been killing birds for the past few weeks.

One coot had such a heavy dose it could barely keep its head above water.

Families on the shore were said to have been appalled by the sight before animal rescuers fished the bird out on Saturday.

Billy Elliott, of Worthing and District Animal Rescue Service, said the incident was unacceptable and rotten corpses of dead birds were a health hazard in a lake that was regularly used for boating.

Worthing Borough Council and the Environment Agency have been investigating the deaths, which might be due to bacteria being released from the silt at the bottom of the lake.

To remove the silt from the lake bed would be costly but Mr Elliott said dead birds and the unpleasant smell of Brooklands were not good advertisements for the town.

He said: "In the past three days, I have taken out a sick duck every morning.

"The Environment Agency has taken water samples but nothing unusual has been found.

"What affects these birds does not happen to them all at once, just one or two.

"Something is being released in the summer and the quantity is just enough to affect a small number.

"This has been happening from August to September for the past five years. We have got to get to the bottom of this to try to stop it."

Mr Elliott hoped the council would make silt removal at Brooklands a priority to save the birds and make the most of the attraction.

He said: "I've taken out more than a dozen dead ducks and coots - some were alive with maggots.

"I do not want to be alarmist but it could take someone getting seriously ill before something is done.

"There is a lack of facilities like Brooklands - it's great for parents with kids.

"People go down there regularly for the playground, the boats and golf course. They are watching these birds hatch, go in the lake and are now watching the birds float by."