With the current heat wave that rolled in over Memorial Day weekend, it feels like summer’s come early for Portland. But for the city’s waterways, it hasn’t. The Portland branch of the National Weather Service recently warned potential river goers that water temperatures could be dangerously low.

“This is a reminder that rivers are still very cold right now,” the agency tweeted on May 28. “In fact, rivers are just as cold as the water along the coast (people wear wet suits in that stuff!).”

Though the Willamette River has warmed up by a few degrees since then, at a peak of 63 degrees, it’s still around 30 degrees cooler than the air.

According to meteorologist Miles Higa, the National Weather Service typically issues a warning whenever there’s unseasonably warm weather and seasonably low water temperatures, a combination that can cause cold water shock.

“Test the waters,” says Higa. “Be prepared and maybe don’t jump right in.”

Besides, the heatwave won’t last much longer. Cooler temperatures should arrive with this weekend, possibly even bringing some rain.

If you do decide to take a dip, the National Weather Service recommends wearing a life vest, avoiding alcohol and being careful around fast flowing water.