The Dickinson County Sheriff's Office said search teams located the body of 30-year-old Chad Lenz shortly after 1 p.m.
Authorities think Lenz jumped into the lake near Pike's Point State Park at approximately 1:30 p.m. Sunday to retrieve an article of clothing that had blown off the boat. His wife and two children were also in the boat.
"We can clearly say that he did voluntarily jump from the boat, but that's about all we're going to be able to say at this time," said Gary Owen, an officer with the Iowa Department of Natural Resources.
Mark Petersen, a dive captain with Arnolds Park/Okoboji Search & Rescue said the boat was stopped -- either in neutral or with the engine turned off -- when Lenz jumped from the vessel. Petersen also doesn't think alcohol was a factor in the drowning.
Lenz was not wearing a life jacket at the time.
Owen said 10-15 mph winds were coming out of the north-northwest at the time of the 911 call. Because swimming abilities vary, Owen said it would be difficult to determine whether choppy waves contributed to the boater's disappearance.
Witness accounts were able to help search teams narrow down the spot where Lenz was believed to have gone overboard. If the missing person can't be found early on, Owen said the chances of a good outcome fade rapidly.
"Typically you look at about an hour, hour-and-a-half, maybe two hours ... after that, you change from a rescue to a recovery operation," Owen said. "We made that change after a two-hour period. We went from a rescue operation to a recovery operation."
Numerous rescue crews continued a more deliberate search until nightfall Sunday.
"It's no longer considered an emergency because there's no potential there of making the rescue, so it slows things down," Owen said. "No longer do we have to be in a hurry. Nothing is going to change. We just have to gather as much information as we can to try to get a close and pinpoint location of where, possibly, the body might be."
Search teams resumed the search at 6 a.m. Monday morning, focusing on a 400-foot by 300-foot area the middle of the lake, in a south-southwest direction of Pike's Point.
Petersen said Lenz was found in 38 feet of water, west and south of Pike's Point and not far from the area where he is believed to have entered the water.
Petersen said searchers considered expanding the search area about an hour before Lenz was found. The teams used side-scan sonar, often used for mapping lake bottoms to find Lenz.
"Then when we have an item of interest -- or something that doesn't look right on the side scan, then we'll deploy divers and check that item out.," Petersen said.
"The challenges today is we (were) having the wind pick up on us along with depth of the water and the size of the lake."
The Dickinson County Sheriff's Office updated the family every two hours. They were given the phone numbers of search team leaders in case any questions arose.
Assisting agencies included: Dickinson County Sheriff's Office, Dickinson County Emergency Management, Okoboji Police Department, Milford Police Department, Spirit Lake Fire Department, Arnolds Park/Okoboji Fire/Rescue & Dive Team
South Central Dive Team from Trimont, Minn. and the Iowa Department of Natural Resources.
"I want to thank the volunteers and the community support is always there," Petersen said. "Everybody leaves work and their families to be able to help and it pays off. On a day it makes you glad you're doing what you're doing -- to be able to help another family out."