Oxygen levels in hundreds of freshwater lakes in the U.S. and across the world are plummeting — and climate change is largely to blame, according to a study published Wednesday.

Why it matters: Per a statement from study co-author Kevin Rose, a professor of biology at Rensselaer Polytechnic Institute: "All complex life depends on oxygen. ... when you start losing oxygen, you have the potential to lose species."

Driving the news: The study published in the journal Natureanalyzed temperature and dissolved oxygen — a measure of how much oxygen is in water — in almost 400 lakes across the temperate zone, mostly in the U.S. and Europe, but also several in New Zealand and one in Japan.

What they found: The researchers found that since 1980, oxygen levels have dropped 5.5% at the surface and 18.6% in deep waters. The fall is 2.75 to 9.3 times faster than the world's oceans.

• Warming temperatures are leading to widespread losses in dissolved oxygen across the studied lakes were linked to climate change and human activity.
• Some lakes saw increasing dissolved oxygen concentrations and warming temperatures, caused by pollution such as agricultural runoff.

Our thought bubble, via Axios' Andrew Freedman: Just as global warming is fundamentally altering marine ecosystems, making ocean waters more acidic, increasing temperatures, and altering ocean currents, it's now clear that sweeping changes are happening in water bodies on land.

• At risk are ecosystems long dependent on a particular temperature and oxygen structure within a lake. In other words, fish and other marine creatures are facing challenges wherever scientists look.

Of note: Researchers have previously documented dissolved oxygen losses in lakes over a sustained period, but "none" have surveyed so many lakes around the globe, noted Samuel Fey, a Reed College biology professor who studies lakes and wasn't involved in this study, to AP.

The bottom line: Rose told AP the conditions researchers observed can "sometimes lead to fish kills" in water bodies.

• "It really means that a lot of habitats for cold water fish could become inhospitable," he said.