Bridger Teton National Forest rangers responded to a call Tuesday when seven teenagers floating on the Hoback River encountered a fallen tree. All were able to make it out of the river, but it was close.

Mary Cernicek, public affairs officer for the Bridger Teton National forest said the obstacle they encountered is called a strainer, which is dangerous because the water rushing past the strainer can upset watercraft, puncture rafts, trap swimmers and even pull someone under.

Dangerous obstacle on the river:

"A strainer can be a downed tree, a log, anything that the water moves in and around and it holds the people up against it, and theoretically it can hold you under the water too, if you're unfortunate enough to be out of your watercraft or a swimmer coming into to one of those with a strong current."

Ms. Cernicek said that people trained in river rescue are taught how to deal with strainers because they can be so dangerous. Another strategy is to scout the river before going into the water and watch for places to avoid.

Scouting river a good idea:

"It was a downed tree with a lot of limbs and branches and it had complete fallen all the way across the Hoback River. And the river constricted at this point; it came around a sharp bend, and if you hadn't scouted it prior to getting on the water, you were pretty much destined to float right into it."

This year's high water has undercut banks, causing the tree to fall across the water. And with the kids who encountered the strainer, Cernicek noted all the teenagers were wearing life jackets.

All were wearing life jackets:

"We were pretty lucky there, and all of those individuals did have their life jackets on and it's something that we can't emphasize enough, that having your life jackets on, while it's not a guarantee, it has been proven to save lives."