Calgary crews are taking steps to remove debris from the Bow River near the Crowchild Trail bridge that is creating a dangerous situation for boaters and rafters.

On Sunday, a number of boaters on the river ran into pieces of concrete and rebar that were submerged under the water on the north side of the river.

Several rafts were punctured by the metal and fire crews had to rescue some of the boaters from small islands in the middle of the river.

Officials believe that the material was likely left over from the 2013 floods and that lower water levels have uncovered the debris.

Fire officials marked the hazardous area and spent the day working to remove it permanently.

“TransAlta utilities is holding back water in the Bearspaw Reservoir to try to drop the river levels. The reason we want to drop the river levels is so that we can cut the rebar down lower so that when we do return the water to normal flow rates, we have a good metre of barrier, of water barrier, between the rebar and the surface of the water,” said Allan Ball, Deputy Chief Calgary Fire Department.

Ball says the operation is quite complex. “It’s a pretty sizable operation. We have a lot of Aquatics resources here and the coordination of it is quite key. We are monitoring the outflow of the Bow right now and we are trying to get it down to the winter flow rates.”

After all the sharp metal has been removed, the water level will be returned to normal and the concrete will be covered up once more.

As for how much space they are looking for in the water to keep boaters safe, Ball says they are looking for three to four feet of water above whatever debris remains.

“The channel we’re working in is about eight feet deep when we have flows of about 100 m3. After we cut this we’re hoping to have a good metre of cushion there.”

Officials expect the operation to take all day on Tuesday, with the Bow River back at normal levels for Wednesday.

Ball adds that a drone will be sent to survey the area sometime next year to determine if there is any more rebar that could present future problems to river users.