The putrid stench began wafting through open windows and on streets on Tuesday, according to civic activist Danny Ruscillo. It continued on Thursday.
Rockaway Park smelled like rotten eggs. And nobody knew why.
Some people blamed the wastewater treatment plant on Beach Channel Drive, which has been known for giving off a smell.
But this time the odor was emanating from a stinky algae bloom in a low-lying piece of marshland in Jamaica Bay, experts said.
"The sulfur smell comes about when we have long periods without rain, high heat and sun," said Dan Mundy Jr., who has spent decades monitoring the bay's activity.
"The problem comes from the very shallow areas of the bay that heat up. Seaweed and bacteria, with the nitrogen in the bay, creates a chemical change," he explained.
The blooms grew inside Pumpkin Patch Channel, a section of the bay just north and west of the wildlife center off Cross Bay Boulevard, he said.
Mundy explained that nitrogen can enter the waterways from any number of sources, including runoff from cars and waste dumped by nearby sewage treatment plants.
Mundy and his father Dan Mundy Sr., along with other advocates, have worked hard over the past 20 years to significantly reduce nitrogen runoff into the bay.
At its peak, 60,000 pounds of nitrogen were dumped into the bay, mainly from the city's treatment plants, the younger Mundy said.
That number is now about 30,000 pounds, although he'd like to see it drop to 20,000 pounds.
"The nitrogen levels in the bay, it's getting better," he said.
The Department of Environmental Protection, he added, has spent millions to improve overflow from nearby sewage plants to lower the nitrogen levels.
It also recently announced a plan to dredge parts of Flushing Bay, near LaGuardia Airport, to help get rid of the rotten egg smell there.
But in Jamaica Bay, he still thinks the city could do a better job.
"We need to continue to see it drop," Mundy Jr. said.
The DEP did not respond to multiple requests for comment, by phone and email.