Anxious family members watched Monday from a nearby hill as dive teams searched an Idaho reservoir for four missing men who may have gone overboard during a prank gone awry.

The men were feared drowned during a boating trip, leaving five young children adrift on the boat in the 87-square-mile American Falls reservoir Sunday evening, authorities said.

The children later told marine patrol deputies that one of the men was standing near the edge of the boat when another one thought it would be funny to push him overboard, Power County Sheriff Jim Jeffries said.

"But apparently, he couldn't swim, so he was immediately in distress," Jeffries said. "The second man jumped in, and so then there were two of them in distress in the water, so the third jumped in and there were three in distress."

Jeffries said the children in the boat were between 2 and 9. One found a cell phone and called 911 after the men began struggling in the water.

The last adult on the boat managed to grab a life jacket before jumping in to try to save the other three, Jeffries said, but he wasn't wearing it and may have only hooked an arm through the device.

Meanwhile, the breezy weather caused the boat to drift away from the men.

Authorities have not released the names of the missing men in order to give their families time to notify other relatives. All were described as being in their 20s and 30s and from Pocatello, Idaho. Two were brothers.

Alcohol was found on the boat, but it wasn't clear if the men were intoxicated, Jeffries said

All the children were wearing life jackets. There were enough jackets on the boat for the adults, but none were wearing them, Jeffries said.

The boat also had a square flotation device that could have been deployed but wasn't, he said.

"I guess panic is a contributing factor," Jeffries said.

The children called emergency workers at 7:40 p.m., soon after the men went overboard, Jeffries said. It didn't take marine patrol deputies long to find them and get them to safety.

Dive teams started their search that evening focusing on an area where a ball cap was found floating on the water.

Stormy weather and nightfall forced searchers to break until Monday, when they used the GPS coordinates from the cell phone at the time of the 911 call and wind speed data to focus efforts.

The water was muddy, and visibility was low, Jeffries said.

"The water's about 45 feet deep, and it's hard to see — you can see your hand, and that's about it," he said. "There's a lot of trees and rebar sticking up in the bottom of the water, and the divers are getting hung up in those sticks and things. It's a slow, tedious process."

The men's families were in shock and struggling to comprehend the tragedy, Jeffries said.

"They have a pastor there with them," Jeffries said.

Search and rescue teams from nearby Bingham and Bonneville counties were assisting, and a four-man crew from the Idaho Army National Guard was conducting a visual search from a Blackhawk helicopter.

Marine deputies were boating with a cadaver-sniffing dog that might be able to detect bodies underwater.