Tucked into the heart of Northeastern’s Boston campus is a tiny oasis from the hustle and bustle of city life. A koi pond, located between the Curry Student Center and Robinson Hall, sparkles in the sun and gurgles as a small waterfall splashes into it. Vibrant, nearly fluorescent koi flash just under the surface.

But what happens to these fish—a dozen or so live in the pond—during the winter?

“They chill out,” says William Detrich, professor of marine and environmental sciences at Northeastern. He means it literally.

Koi are ectothermic, Detrich says, which means their body temperatures are determined by the ambient temperature, in this case, the temperature of the water in the pond on campus. As the water cools, so do their bodies.

And, as their bodies cool down, their metabolisms slow to the point that they hardly need any energy at all—at around 40 to 50 degrees Fahrenheit, the koi stop eating altogether, Detrich says.

The fish will congregate near the bottom of the pond, where the water remains liquid even if the surface is frozen, and they’ll enter a state called “dormancy,” Detrich says, in which they mostly stop moving, and nearly stop expending energy.

“They literally chill out, and just wait for the pond to warm up,” he says.

The good news is that, even in their dormant state, the koi are a sight to behold. Adirondack chairs and newly installed fire pits surround the pond, creating a peaceful place to work, study, or simply spend some time outside.

On a chilly January day, Pauline Murphy, who lives in the nearby Roxbury neighborhood, was doing just that.

“I love these fish—I come here all the time, and even bring my friends to look at them,” she said. Murphy had just closed the book she was reading, and paused to take a look at the dormant koi.

The fish’s tiny movements were, to Murphy and this News@Northeastern reporter, quite mesmerizing.

In a quiet moment of wonder and appreciation, the stress of the day seemed to drift away. All that was left were delicate puffs of steam that rose out of our masks, and the koi, gently resting.

For media inquiries, please contact media@northeastern.edu.