AUSTIN (KXAN) — The foul-smelling water plaguing downtown and south Austin since Thursday morning is not just due to the presence of Zebra mussels, but rather dead Zebra mussels, according to Austin Water.

Austin Water uses chemical retardants in its piping systems and raw water tunnels that help slow the population of Zebra mussels. One of the raw water tunnels at the Ullrich treatment plant was taken out of service temporarily for a capital improvement project.

According to Austin Water, in the time this raw water tunnel was out of service, Zebra mussels infested the line in unprecedented numbers. When the tunnel was brought back into service, the chemical retardant killed the mussels, causing the smelly water.

“We’ve been preparing our chemicals. We just did not anticipate how fast they could infest our piping system,” said Greg Maszaros with Austin Water. “We don’t have a lot of experience with them here but clearly we’re learning from that.”

Austin Water tells KXAN that, while the water was emitting a smelly odor, it was still safe to drink, due to the fact that they constantly disinfect their systems, killing harmful bacteria or organisms. 

The water company is working with an outside consultant, the engineering firm Black and Veach, to develop a copper-ion system to further slow the growth of the zebra mussels. While the new system is being developed, Austin Water will have to undergo mechanical cleaning of the mussels, which means someone will be physically scraping them off piping systems and raw water tunnels.

The smell is being eliminated thanks to the addition of activated carbon into the water. According to Austin Water, they use a numerical index to rate the smell. On Thursday, the smell was at a nine, and on Friday Austin Water tells KXAN the smell has dropped to a one.