The two detention basins that Moorpark officials were surprised to learn were filled with stagnant water in March still hold the same level of water today.

Residents worry the basins on property owned by Shea Homes are a health and safety risk. Teens are still hopping the fence to play in and around them. People have been seen fishing and boating in one of the ponds that is meant to drain to the Arroyo Simi nearby.

"The kids can still get in there. They're still climbing over the fence," said Derek Bovard, a nearby resident.

And then there is the potential for a mosquito breeding ground in the stagnant water, at a time when West Nile virus has been found in the county.

City Engineer Yugal Lall said earlier this year that the basins are meant to hold water only when it rains. Moorpark had 4.74 inches of rain this season, on pace to be the driest year on record.

But Lall now says the basins — one the size of a small lake — are expected to hold water because the Arroyo Simi runs at the same level as the bottom of the detention ponds. The Arroyo Simi collects runoff from developments east of Simi Valley, which then goes to the ocean. He called them "natural and expected" occurrences.

"It's high groundwater," Lall said. "That's what it's supposed to do."

Residents worry the water could be filled with bacteria or draw mosquitoes.

The city's Animal and Vector Control Division has had the ponds on its radar for a while, said the division's Mark Westerline. The city put fish meant to eat mosquitoes and insects in the ponds.

"I looked in the area about a week ago," Westerline said. "We periodically check over there to make sure there are no problems."

The ponds are south of Los Angeles Avenue between Spring Road and Moorpark Avenue on property that was meant for 77 new homes. But that project has been on hold since the release of draft flood plain maps by the Federal Emergency Management Agency two years ago. Only 20 homes and four model homes have been completed in the Shea Homes Canterbury Lane community.

City officials questioned the accuracy of the new flood maps last year and appealed to FEMA. It is unclear whether Shea Homes would continue to build or would have to change or abandon the project.

A reinforced fence was built by the developer, and a part of the path leading to the larger pond has been blocked off in recent months. While the fence surrounds the overall property, there is no barricade around the individual basins, which have steep edges.

But at least the city is monitoring the ponds for mosquitoes, Bovard said.

"We still have a lot of questions, but it's good to know they put fish in there," he said.