What’s that smell? Lakes reek of decay — but it’s totally normal, national park says

Lakes might start reeking of decay — but it’s completely normal.

An annual phenomenon could make lakes smell like rotting, decaying matter, Glacier National Park said in a Facebook post on Monday.

Usually the bottom of any lake is much colder than the top because the dense water sinks to the bottom. But as the air in places that have cold winters becomes frigid, the surface of the lake starts to cool down.

“These layers of temperature can prevent nutrients and oxygen necessary for life from cycling throughout the lake,” the park said. “But twice a year — once around now, and once in the spring — that can change.”

The surface water can sometimes cool down so much that there’s a bit of time where the top and the bottom of the lake are the same temperature — and it stinks.

“When this happens, the lake can ‘turn over,’ mixing in oxygen throughout the water column before ice forms and seals it away for the winter,” the park said. “You can’t really see it happen, but in some lakes, you can smell it.”

The stuff decomposing at the bottom of the lake makes the air smell like “sulfur and decaying matter.” It’s “less than pleasant,” the park said.

“Luckily that odorous phenomenon isn’t too common here in Glacier,” the park said, “but you may have experienced it elsewhere!”

This story was originally published November 10, 2020 at 1:13 PM with the headline "What’s that smell? Lakes reek of decay — but it’s totally normal, national park says."