Environmentalists say the Great South Bay is dealing with the worst brown tide it has seen in 30 years.

Experts say the algae bloom that began in mid-May is well into its second month. They say prolonged blooms can result in the death of small hard clams and seagrass, two key components of the Great South Bay ecosystem.

Rebecca Resner, the hatchery manager at the Great Atlantic Shellfish Farm in East Islip, says the baby clams and oysters they are trying to grow are being suffocated by the brown tide. 

"The brown tide stunts the growth of our shellfish, and at the levels it is now, it can cause mortality," she says. "Shellfish have to filter water to survive."

Brown tide is caused by an overload of nitrogen in the water. It has been linked to fertilizer runoff and antiquated cesspools.