A few months ago Aaron Aafedt of Belgrade dug out a small pond on his property. He needed the gravel for a shop he was building, and he wanted a pond where he and his young children could enjoy a little of the outdoors close to home.

“I just did it because I really enjoy fish,” he said.

Aafedt is hardly alone. Gallatin County has seen a steady increase in recent years in the number of permits and certificates of completion issued to local landowners for man-made ponds. Montana Department of Natural Resources and Conservation records show that state officials approved 36 in Gallatin County last year, up from 10 ponds in 2000.

So far this year, they have approved 18 new ponds.

“There is a huge increase in the interest in having ponds,” said Marnie Johnson, co-owner of Montana Ponds of Bozeman.

Landowners build and use ponds for a variety of reasons, from creating reservoirs for fighting fires to, in the case of a large pond outside Manhattan, a place for jet skiing. Many landowners also stock ponds with fish for a little close-to-home angling. In those cases, they are required to get a non-commercial private fish pond license from the state Department of Fish, Wildlife and Parks.

Only one other county in the state, Ravalli, has more registered ponds than Gallatin County. Since 1973, the state has approved 304 ponds in the county, and given that many landowners don't bother with the regulatory hoops, state officials said, the reality is there are likely more out there than the numbers show.

That growth has sparked concern among some residents and environmentalists who say man-made ponds provide a potential avenue for water depletion in an area where water is supposed to be tightly regulated. Also of concern is the potential for the man-made ponds to serve as beachheads for fish diseases and invasive species.

Bob Snyder, the fish hatchery bureau chief for Montana Fish, Wildlife and Parks, said one of the biggest impacts of ponds is the sheer volume of water they need.

“They are competing for water that our wild fish need in the streams and rivers,” Snyder said.

Snyder also recalled a case where a private pond was linked to an outbreak of whirling disease on the Lower Clark Fork River.

Pond builders and users are required to follow many of the same state rules for uses of other sources of water. Landowners must get a beneficial water use permit from the DNRC if they plan to divert surface water to fill a pond or use a well pumping more than 35 gallons a minute or 10 acre feet of water a year.

Wells that pump less water than that don't need a beneficial water use permit, so a landowner who uses one to fill a pond needs only to turn in a certificate of completion after digging out the pond.

A typical pond will lose 2 acre feet of water to evaporation a year for every acre of surface area, said Alan English, manager of the Gallatin Local Quality Water District. One acre foot comes out to a little less than 326,000 gallons.

That doesn't necessarily make ponds the biggest consumer of water; an irrigated lawn can lose up to 1.55 acre feet a year of water for every acre of lawn, English said.

Ponds can be designed to minimize water loss. Companies such as Montana Ponds and Pond and Stream Consulting Inc. of Bozeman work with landowners to build properly permitted ponds that cut down on water consumption. One technique mentioned for minimizing water loss is using pond liners.

Sometimes their job involves correcting mistakes by landowners who tried to do it themselves.

“There are people who are in Montana who think you can do what you want to do, and we've fixed a few ponds like that,” Scott Davis of Pond and Stream Consulting said.

Improperly designed ponds might also benefit invasive species at the expense of native species.

The typical bowl-shaped pond with steep edges is a perfect breeding ground for invasive bullfrogs, who will lay their eggs in deep water, said Bryce Maxell, senior zoologist for the Montana Natural Heritage Program. Native amphibians need shallow water to breed, so steep-edged ponds really don't do them any good.

The Montana Watercourse, a statewide water education program housed at Montana State University, has put together a guidebook for designing ponds to minimize their environmental impact. The guidebook is available by calling 994-6671 and on the Web at www.mtwatercourse.org.