PROVIDENCE — For weeks one of nature’s spectacles has been taking place in the shallow rivers downtown, yet few people seem to notice.

Thousands of adult menhaden, swimming in vast, slow-moving schools, have filled the Providence River in front of the Rhode Island School of Design and even ventured up the Woonasquatucket River into the upper reaches of Waterplace Park.

A few dozen fish have died and floated to the surface.

But thousands more swim languid formations, turning one way and then the other in the waters. Students and office workers walked by yesterday just a few feet away, but few stopped and looked.

Stephen Quartino, a Treasury Department employee, was crossing the Crawford Street Bridge on his way to the Rhode Island attorney general’s office when he said he saw a flash in the water that made him look down.

He spent a few minutes looking down at a swirling mass of fish. Every few seconds one fish would peel off from the school and make a silvery flash to the surface.

“It’s kind of neat seeing wildlife in the river. You don’t expect it. Maybe Buddy did fix things up after all,” Quartino said, referring to former Mayor Vincent A. Cianci Jr.

Jennifer Pereira, executive director of the Woonasquatucket River Watershed Council, a group working to revitalize the river, saw the menhaden while canoeing on the river a few weeks ago.

“We were astonished,” she said. “I think it shows how things have improved with so many people working to clean up the river.”

On the same trip, she saw people fishing in Waterplace Park. They were fishing for the bluefish and stripers that feed on the menhaden.

The menhaden are probably in the rivers because their numbers have soared so high all over Rhode Island, says April Valliere, a biologist in the Department of Environmental Management’s Marine Fisheries Division.

“They are everywhere,” said Valliere. There are huge schools in the Blackstone River, near Jamestown in Narragansett Bay, and along the south shore, where they have been driven up onto the beaches by bluefish and stripers.

Charter boat operators also have reported huge schools of bluefish in the Bay in recent weeks.

No one can explain the sudden upsurge in menhaden. But it comes on the heels of a battle between recreational and commercial fishermen that focused on who would get to catch them.

One commercial fisherman trawls Narragansett Bay each summer to catch menhaden to sell as bait to local lobstermen. Recreational fishermen believe the commercial boat takes too many fish and that cuts their take of bluefish and stripers.

The recreational fishermen got a bill introduced in the General Assembly earlier this year that would have banned commercial menhaden fishing in the Bay. The bill didn’t pass, but it did trigger some emotional reactions from local lobstermen, who feared they would lose a cheap source of bait.

The DEM limited commercial catches and ordered its staff to study local menhaden populations.

Valliere says the menhaden usually leave the Bay in September. She doesn’t know why there are so many still here, but it may be the warm weather.

That same warm weather has her a bit worried about conditions in the rivers. She hears reports that some of the fish are dying, but the flow of river water appear to be keeping oxygen levels up enough to support the big schools.

Last week, there were also reports of big carp in the rivers, she said.

“This is the first time in years we’ve had such big concentrations here,” said Valliere. “It’s gotten everyone’s attention that there are so many and they are remaining.”

Today is supposed to be hotter than yesterday. Valliere hopes that doesn’t harm the fish.

The DEM and Rhode Island Sea Grant have scheduled a daylong science and policy symposium on allocating menhaden for Nov. 30 at the University of Rhode Island’s Graduate School of Oceanography. The symposium is free, but registration is required. Call (401) 874-7599 or write to bsomers@uri.edu.

plord@projo.com