From a distance, they look like giant insects skimming across the surface of North Park Lake.

Up close, they suggest science fair projects gone slightly wrong.

Hydrobikes consist of a bicycle frame mounted above two long pontoons. They are strictly human-powered. When the rider pedals, a chain drive turns a propeller. The craft steers like a bicycle, with the handlebars turning a front-mounted rudder.

Unpadded seats are adjustable to compensate for riders of different heights. Climb aboard and your weight is naturally centered between the pontoons, producing a very stable, if slow, ride.

	Robin Rombach, Post-Gazette August Franzen, 9, removes vegetation from the propeller of a hydrobike on North Park Lake to keep the craft moving. This is the first year the hydrobikes are available for rent at the park. August, of Regent Square, was riding with his father, Nathan Franzen. Click photo for larger image.

"Top speed of about 10 mph," according to Larry Beighey, of New Brighton.

Mr. Beighey, known as "Hydrobike Larry," is a former construction worker who found a second career renting, selling, leasing and tinkering with the vehicles that gave him his nickname.

Hydrobikes are suitable for anglers, too. "You can stand on one of the pontoons and fish all day," Mr. Beighey, 55, said.

"This is the fourth year I've been renting hydrobikes. I've never had anybody fall off or get hurt."

In addition to renting hydrobikes at North Park, he runs the boating concession at Beaver County's Bradys Run Park.

Hydrobikes are not cheap, selling for about $1,500 each, which is why Kayak Pittsburgh North opted to lease them from Mr. Beighey when it began to manage the North Park Boathouse this summer.

Kayak Pittsburgh is an affiliate of Venture Outdoors, a regional nonprofit organization that seeks to encourage people to participate in open-air activities.

Business at North Park has been good, and the weather has cooperated, said Jon Lucadamo, program director for Venture Outdoors. "We've lost maybe a half-dozen days," he said. "We're getting a lot of positive feedback."

Robin Rombach, Post-Gazette Laura Stiles, 14, left, paddles a kayak on North Park Lake, while her sister, Michelle, 11, and father, Joel, ride in another. The McCandless family rented the kayaks from Kayak Pittsburgh North, which began managing the North Park Boathouse this summer. Kayak Pittsburgh North is an affiliate of Venture Outdoors, a nonprofit group that encourages outdoor recreation. Click photo for larger image.

Kayak Pittsburgh North has a three-year contract with Allegheny County to provide rental watercraft at the park. Its fleet includes one- and two-person kayaks, canoes and rowboats in addition to the hydrobikes.

Mr. Lucadamo said the only negative comments he had heard had come from disappointed visitors who wanted to rent paddle boats, which are not available. Many recalled riding in such craft when they were children.

Mr. Lucadamo is getting prices on replacement paddle boats, but he said he couldn't promise delivery this year.

Mr. Beighey was an active kayaker until an accident shattered his right arm, making it impossible for him to paddle.

Hydrobikes allow him to get back out on the water. "I like quiet, nonpolluting, environment-friendly water vehicles," he said.

As North Park Lake continues to fill with silt, aggressive plants, including waterlilies, have filled more and more of the man-made lake. The plentiful vegetation can make pedaling difficult as leaves and stems from water plants twist around the propeller blades and housing.

Each hydrobike has a lever for bringing its prop out of the water so it can be cleaned. During a recent hour-long excursion, the propellers had to be cleaned about a half-dozen times.

Always the tinkerer, Mr. Beighey has fabricated an underwater weed-whacker from PVC pipe that he hopes Allegheny County and Kayak Pittsburgh will allow him to try in the lake. The device is designed to travel across the shallow, silty bottom of the lake, roll up weeds and pull them out by their roots. The result would be a vegetation-free 10- to 12-foot corridor through the lake, he said.

"The present conditions don't do the bike justice," he said.

"North Park Lake is really bad with weeds."

Kayak Pittsburgh North operates from 11:30 a.m. to 7:30 p.m. seven days a week, weather permitting, in the North Park Boathouse. The rental rate for canoes, rowboats and hydrobikes is $10 an hour. Solo kayaks are $12, and tandem kayaks are $15.

For information, call 724-935-1968 or see www.kayakpittsburgh.org.