After a late ice-out and slow spring warmup, Minnesota lakes appear to be approaching safely swimmable temperatures just in time for the July 4th holiday.

Lake Minnetonka, where surface water temperatures were running in the mid-80s at this time last year, crossed into the 70s Tuesday for the first time in this spring’s bi-weekly measurements. There was a 14-degree leap since June 11 in the area between Wayzata and Orono.

The state Department of Natural Resources considers water below 70 degrees to be “cold,” said Kara Owens, a DNR boat and water safety specialist.

“Of course we want to jump in, but when you have that warm, warm air, jumping in a lake below 70 degrees can still cause a shock on your body,” Owens said.

Statistics on normal lake temperatures are scarce, but officials say it’s clear from both fish and human behavior that lakes have warmed up much more slowly this year than usual.

About 25 miles north of Brainerd, the temperature on Pelican Lake has been averaging about 77 degrees in recent days, said Tyler Blong, manager of the boat marina at Breezy Point Resort. But it broke into the 70s only last week, and is probably much colder in deep areas, he said.

“Two weeks ago, no one was swimming,” Blong said.

Of course, the bigger, deeper and more northerly the lake, the colder it is likely to be. Lake Superior’s temperature at Duluth’s Park Point on Thursday was an intimidating 53 degrees.

Owens noted that the St. Croix River at Stillwater also crept above 70 degrees in recent days, but high water and heavy flows remain the more serious concern there, as well as on other regional rivers, she said. A no-wake zone has been imposed on the St. Croix from the mouth at Prescott, Wis., to Taylors Falls, Minn.