The Minneapolis Park and Recreation is considering building a new public pool-lake hybrid - the first of its kind in the country – in Webber Park in north Minneapolis. Instead of chlorine, the swimming hole would use wetland plants and a biological filter to purify the water. It's such a new concept that the park board would need special permission from the state, although similar pools are already in place in Europe.

During the Webber Park design charrette that began in September, several design ideas were discussed by community members and designers including using a natural filtration system for the new pool.

The Minneapolis Park and Recreation Board has been getting community input about Webber to guide $4 million in improvements, which should include plans for a new aquatic amenity. Concepts discussed at the recent multi-day design event were recently updated on the Webber Park master plan page. About 60 percent of those at the meetings said they were supportive of natural treatment, said Bob Schunicht, vice president of Landform, the Minneapolis firm hired to develop the master plan for Webber Park. There aren't any public natural swimming pools in the U.S. right now, though there are some in Europe, Schunicht said.

A natural swimming pool is not quite a lake and not quite a pool, said Jennifer Ringold, manager of community engagement and citywide planning for the park board.

"This is somewhere between the two," she said.

According to BioNova, a company that builds natural swimming pools and is partnering with Landform, chemicals aren't used nor are there any devices used that would disinfect or sterilize the water in a natural swimming pool. Instead, the water is cleaned by a biological filter and the regeneration zone, which has plants that help clean the water. The "swimming" and regeneration" zones can be united or the regeneration zone can be either partially or completely separated from the "swimming" part of the pool. See below for a diagram of how it could work.

If the filtration system was approved by the park board, the park board would make a request to the state of Minnesota for a pilot project, Ringold said. It would need to be a pilot project since the Minnesota Department of Health doesn't currently have regulations for natural swimming pools, though there are restrictions for beaches at lakes and conventional public pools.

The park's pool facility, which was built in 1979, was closed for the summer due to structural and mechanical concerns. It would be replaced by some type of aquatic feature, though a decision about what type and what kind of filtration system is still up in the air.

A cost comparison has to be done for the different types of filtration systems, Ringold said. Generally, construction of a pool with a natural filtration system versus one with a conventional filtration system should cost about the same, Schunicht said. Maintenance of a natural pool could cost less since it doesn't have to be treated by chemicals, he said.

There should be at least one more community meeting about design ideas for Webber Park possibly in December, Ringold said. A new pool is planned to be built in the spring of next year and opened in the summer of 2013.