SOUTHAMPTON - Long Island's bays are normally sun-dazzled summer playgrounds, but some of them are facing serious trouble.

For the sixth consecutive year, the brown tide is back. Murky water bursting with algae is washing up along the South Shore, most recently in parts of the Moriches and Shinnecock bays.

Brown tide is caused by excessive algae. The microscopic plant cells suck oxygen from the water and choke off eelgrass, a natural incubator for many underwater species. Environmental experts say the algae are feeding off of excess nitrogen in the water, mostly leaching from cesspools and home septic tanks.

The nitrogen from these wastewater systems has been found to be slowly moving through the Island's groundwater and into the bays, spiking algae growth.

Experts say brown tide is safe to swim in, but it does a number on shellfish populations. The algae blooms are threatening the livelihoods of local fishermen who are concerned that their usual spots will be shut down because of the problem.

Activists say a good start for dealing with the problem would be to require state-of-the-art sewage treatment systems for all new development, especially near the shore. Others are lauding shellfish nurseries that aim to jump-start the recovery of the bays.