A wildlife habitat may be under threat from flood defence works designed to protect the coastline.

Widewater Lagoon in Lancing supports a wide range of plants, animals and rare birds including ospreys.

The beauty spot relies on maintaining a balance of seawater, which filters into the lake through the shingle beach separating it from the sea at Lancing Beach, and fresh water which enters the lake from its northern side.

The waters mingle to form brackish water.

Campaigner Derek Neate, of the Friends of Widewater Lagoon, warned this balance could soon be upset if the Environment Agency went ahead with plans to improve flood defences by building up shingle on the beach.

The work, designed to protect low-lying homes from flooding at high tides, would stop seawater percolating through to the lagoon.

Not only would this upset the balance of salt and fresh water, it would also deplete water levels, putting the lagoon at risk of drying up in summer.

Mr Neate said: "If you interfere with Mother Nature and end up with too much salt, or not enough salt and too much fresh water, the balance will go and we will lose what is growing and living there."

The Environment Agency is proposing to ensure Widewater continues to have a supply of salt water by running a pipe through the sea defences to the lake.

But Mr Neate said: "Their idea of balance is to put a great big pipe at one end to let pure salt water in instead of it percolating through the shingle. It will kill off the lagoon from that end. This could be the death of the Widewater.

"The sea wall has never been topped and if it does, there is no danger to property or people because the water would just go into the lagoon."

Rupert Clubb, Sussex flood defence manager for the Environment Agency, said: "If we did not do any work to the sea defences, in time Widewater would disappear and so would the houses nearby.

"Their primary defence is the shingle bank and we need to maintain it.

"We could not just leave a gap in the defences at Widewater with everything improved to either side, it would be quite dangerous. The land is very low there and without sea defences there would be flooding."

Jon Curson, conservation officer for English Nature, has been working with the Environment Agency on its plans.

He said: "We have asked for some mitigation measures. The main one would be putting a pipe or pipes with filters to allow salt water to get into the lagoon. It would have a valve so we could stop it working if the lake was getting too saline."