DAVIS (CBS13) — Aside from COVID, there’s another health danger for UC Davis students—one that’s easy to see just by walking through campus.

As students and staff return to campus this week, they are being warned about a toxic substance lurking in the campus waterways.

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The danger? A layer of green slime covering a mile-long portion of Putah Creek that runs from downtown Davis through the center of campus.

The creek has no natural flow.  All the water comes from storm runoff and discharges from the water treatment plant.

“When you have virtually stagnant water, you get a lot of algae growth—particularly surface algae as well as cyanobacteria,” said Andrew Fulks with the UC Davis Arboretum.

That’s a toxic organism that can cause serious health problems.

Hazard signs have now been posted, warning people to avoid exposure and keep their pets out of the water.

“It tends to happen in the summer after we’ve had a long dry period and a long hot period,” said Nina Suzuki, a UC Davis waterway steward.

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But there’s hope on the horizon.

The campus just received a five million dollar state grant to improve water quality by installing a series of weirs and recirculation pumps that will prevent algae blooms.

“This project is going to transform this waterway,” Suzuki said.

A portion of the project is already complete, and they’re seeing success.

“It does aerate the water that goes over the weir, and so often times we find fish that gather right there at the weir because the higher oxygen water makes it easier for them to breathe,” Fulks said.

It’s an effort to enhance the wildlife habitat and keep it safe for people and their pets.

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Total restoration costs are expected to be around $8 million and it should be finished by 2023.