Bayman Ed Warner knows that when the red water shows up, all the fish leave the bay.

Like many Long Islanders, he's had enough of the brown tides, red tides and rust tides that are choking local bays and harbors. Experts say the number one cause is excess nitrogen seeping from cesspools and septic tanks.

To reduce nitrogen, Suffolk requires commercial businesses to use advanced wastewater-treatment systems or connect to sewers. But a News 12/Newsday investigation shows that hundreds of businesses have been able to avoid those requirements by using a legal loophole.

Many properties are simply "grandfathered in" from before the county toughened up its sanitation code back in 1981. Owners of properties with buildings built before that time can expand or rebuild, without putting in an advanced wastewater treatment system. Experts say it means two to three times more nitrogen heading into the groundwater, and eventually into streams and bays.

"It's basically permitting pollution," says environmentalist Kevin McAllister.

Suffolk grandfathered a posh new condo complex on the grounds of a former motel in Hampton Bays. The owner told News 12 Long Island that he replaced the old cesspools with new septic tanks and leeching areas. But the system does not significantly cut nitrogen.

Environmentalists say it's unacceptable that the project had to conform to all new building codes, yet is allowed to have sanitary systems using "1800s technology."

Suffolk County Executive Steve Bellone has declared water protection his number one priority. County officials admit the grandfathering rules are far too lax, and they say they've proposed reforms that would cut the number of grandfathered polluters.

Businesses worry that the new wastewater requirements will be too expensive without some kind of government subsidies.

But critics say the changes don't go far enough, and time is running out. They say the pristine waterways that make Long Island so beloved are in serious trouble.