A few days ago, Erin Devine and Mary Maupin stopped on a trail in Manito Park and looked down into the murky green water of Mirror Pond.

“We were like, ‘Wow, that’s pretty gross,’ ” Maupin said.

Visitors to the pond have for years complained about its fluorescent green hue and occasional odor, and volunteers and city officials have spent as long working to clean it up.

But with abundant duck poop and little water circulation, summertime algae blooms keep coming back.

“What we’re looking at now is a long-term solution,” said Garrett Jones, the city’s park planning and development manager.

As early as this winter, Jones said, his department could begin designing a filtration system for the pond. The water would run through underground pumps and filters before returning to the pond through pipes or waterfalls.

A consultant hired by the city in 2010 estimated that a built-in filtration system would cost about $308,000. Jones said the actual price likely will be higher due to inflation.

Jones said waterfalls would have the added benefit of aerating the water. And more trees and plants would provide shade and help lower the temperature of the water, slowing algae growth, he said.

In the meantime, crews are putting the finishing touches on a new asphalt walkway that helps reinforce the southern and western banks of the pond, preventing sediment from clouding the water.

Jones said that project took priority over the filtration system because the city, with fundraising help from the nonprofit Friends of Manito, was able to secure a $90,000 matching grant from the state Recreation and Conservation Office.

Park staff members also are testing a small aerator that could be seen floating on a raft in the pond Monday afternoon. Jones said that’s part of a pilot program and not related to the broader restoration plans.

There’s still too much duck and goose poop, which feeds the algae, which depletes dissolved oxygen in the water, which makes the pond a less hospitable place for fish, frogs and other aquatic life.

The problem got so bad that, in 2008, park staff corralled and relocated 35 ducks that had been living off bread handouts in the pond.

City code now prohibits people from feeding the waterfowl, and there are signs explaining that around the pond. But park staff members still routinely need to ask visitors to stop, Jones said.

“We’ve done a really good job of trying to educate the public about feeding ducks and the effects of that,” he said. “We can have all the signs in the world, but the face-to-face education is what’s really effective.”

On Monday afternoon, Larry Benson of Fort Lauderdale, Florida, visited Manito Park for the first time.

“It is awfully green,” he said, staring at the pond. “I’d love to have it clear like a swimming pool. But the park itself is gorgeous. It’s beautiful.”