Oak Cliff mountain bikers and trail runners say something smells like sewage at Oak Cliff Nature Preserve.

Besides that, streams in the park look polluted.

The Texas Commission for Environmental Quality was onsite Monday, “and observed an unknown discharge from a city storm drain,” the agency’s public information office reports.

From TCEQ spokeswoman Martha Otero:

“The city of Dallas is investigating the discharge to determine what it is and where it came from, as well as working to clean it up. The City of Dallas … has primary jurisdiction. The TCEQ will remain in contact with the city to ensure this issue is resolved.”

The city’s office of Stormwater Management has not yet responded to our emails.

The 6.5-acre park is owned by the Texas Land Conservancy.