Fall means the return of brown tide to the Great South Bay, and the harmful algal bloom is expected to be worse than previous seasons.

Dr. Chris Gobler studies the shellfish-killing blooms that are impacting Long Island's coastal waters.  He says the outbreak of brown tide this late in the seasons is bad news.

“We are seeing it essentially from the Great South Bay all the way to Shinnecock Bay,” says Gobler.

Just south of the LI Maritime Museum in the Great South Bay is the epicenter of the brown tide bloom.

“There it's over a million cells per milliliter," says Gobler. "We have never seen that in October.”

Gobler says the murky brown water, which is lethal to shellfish, is caused by a nitrogen-loving algae. Gobler blames the excessive nitrogen in our bays and estuaries on lawn and farm fertilizer runoff and old cesspools and septic tanks that line Long Island's shoreline. Gobler also points to climate change as a contributing factor.

Gobler says updating sewage septic systems and stopping use of fertilizers is the only way to combat brown tide.