The heat building under Minneapolis is not just in the air. New measurements and long-running studies indicate the groundwater beneath the city is warming, a trend that could ripple up into cherished springs, coldwater streams and even aging pipes. Geologist Greg Brick and other researchers have logged temperatures at Coldwater Spring and in underground voids beneath downtown that sit several degrees above historical baselines, raising fresh questions about what a warmer aquifer might mean for fish, plants and public health.
According to MPR News, Brick measured groundwater emerging at Coldwater Spring in November 2025 and told reporters he has observed warming beneath the city. The outlet set his observations alongside university monitoring and long-term records that together suggest Coldwater Spring has been running warmer in recent years.
Those newer readings contrast with much colder historical measurements. In 1836, Joseph Nicollet’s notes put Coldwater Spring at roughly 46°F (about 7.8°C). Monitoring by the University of Minnesota from 2013 to 2015 found temperatures in the low teens Celsius. The multi‑year data set on temperature, chemistry and flow at the site is compiled in a thesis from the University of Minnesota.
How the city heats what’s below
Researchers say the source of the extra warmth looks urban rather than deep and geothermal. Heat bleeding off pavements, basements and warm stormwater can conduct downward into shallow aquifers and nudge up spring temperatures. Greg Brick describes that mechanism in work focused on the Minneapolis subsurface, while global studies of subsurface urban heat islands, including research by Menberg et al., 2013, report similar patterns in cities elsewhere.
Risks to springs, fish and pipes
Warmer groundwater is not just a curiosity on a thermometer. Scientists note it can reshape stream and spring ecology, stress coldwater species and alter chemical and microbial processes. Process‑based research shows that streams dependent on cold groundwater inputs are especially sensitive when that cool inflow is reduced, with summer temperature peaks rising noticeably as a result. Studies from the USGS highlight that vulnerability, and local experts have warned that warmer subsurface water could intensify microbial risks during water‑main breaks…