A 46-year-old Big Lake man died Sunday, three days after he suffered electrical shock while charging a boat battery as he stood in the shallows of Sherburne County's Eagle Lake.

According to the Sheriff's Office, Daniel Petersen was standing in about 20 inches of water on Thursday, the July 4th holiday, when he lost his footing and fell into the water while holding the battery charger. When his sister, Kris Biser, 49, saw him fall, she ran into the water to try to help him and also was shocked.

Deputies called to the scene in the 23000 block of 188th Street just after 2:30 p.m. that day administered CPR to Petersen, who then was airlifted to Hennepin County Medical Center in Minneapolis. Biser, who was breathing on her own after neighbors rendered first aid, was taken by ambulance to St. Cloud Hospital.

Kara Owens, boat and water safety specialist at the Minnesota Department of Natural Resources, said electrocution drownings are "very rare."

They're more likely to happen in a marina because of the electrical currents between the boats and the dock, and they only happen in fresh water, she said.

The DNR doesn't keep a comprehensive list of electric shock drownings (often times the individuals die before going underwater, so a state drowning report isn't filed), but a couple have been reported in Minnesota in recent years.

In July 2012, while working on his boat lift in Willmar, a 56-year-old man died after he came into contact with an extension cord that had been rubbed bare and fell into the water, according to Kandiyohi County Sheriff's Office.

And in May 2011, a 50-year-old Lake City man drowned in Lake Pepin, in Wabasha County, when he tried to rescue his dog in the water, but was knocked out by an electrical shock from a boat lift.

Anyone recharging a battery should do it on shore, Owens said.

"It's just a good reminder for people out there to know that water does carry electricity."