Every year the City of Austin comes out with an environmental assessment to keep officials up-to-date on air quality and the condition of the city’s waterways. Beyond those big issues, you can also find some stranger stories about pollution and cleanup-related issues in Austin.

Milk sludge

You might not know it, but the city has a 24-hour hotline you can call to report possible pollution spills or other environmental concerns. Last year, the team that answers those calls found itself responding to a spill of so-called milk sludge after a “catastrophic failure” at the Borden Dairy plant along the Colorado River.

“It came from the processing plant and it was a solid, this sludge, it was like a solid material that got into a storm sewer pipe and it was washed down through the storm sewer into a nearby creek,” said Chuck Lesniak, the City of Austin’s environmental manager.

The report says the city was alerted and managed to get the company to contain and clean up the spill.

Hidden garbage caves

Austin's early farmers and ranchers filled underground caves all around the city's west side with garbage.

“Ranchers worried about their animals falling into these caves,” Lesniak said. “They would fill them in, or they filled them in, to provide more level farmland.”

The makeshift landfills also deterred trespassers. The report says 163 caves were documented in Austin.

The city acquired the Wade, Hideout and Maple Run caves in the '90s, and the report suggests it’s looking to open up some of them to the public. The report touts the caves’ ability to allow rainwater to flow more easily into area aquifers.

KUT's Nadia Hamdan and Mose Buchele talk about the city's annual environmental report

Zebra mussels

Invasive zebra mussels, which arrived in Austin last year, can hurt water quality, kill off other wildlife and ruin water treatment infrastructure – and, unfortunately, the rapidly spreading bivalves are flourishing in Texas lakes.

The report says state and local scientists are putting together a plan to monitor the mussels' spread in Austin.

Austin’s carbon footprint and the big picture

As for Austin’s emissions, the only category in which the city has seen an increase is in industrial output, which jumped 63 percent, according to the report. But, because Austin is not a very industrial city, that makes for a small part of its total emissions.

As far as air and water quality goes, the report says ozone levels were up a little bit last year, but the city isn't violating federal standards. Water quality in Austin's creeks and rivers seems to be improving, though that could be thanks to the relatively rainy years we've had lately. Both Lady Bird Lake and Lake Austin had improved water quality, as well.

Read the full report below.