Last updated at 11:59 p.m. on Thursday, Feb. 22, 2018 with additional information.
At least tens of thousands of dead and dying fish were found in a small creek off Dupont Parkway near the Tennessee River Wednesday, launching an investigation Thursday morning.
The cause of the incident is up for debate. The investigating agencies — Tennessee Wildlife Resources Agency and Tennessee Department of Environment and Conservation — have not determined a culprit, but city officials and Tennessee Valley Authority biologists believe the incident is weather related.
"At this point, officials believe that the cause is related to weather occurrences earlier this week, including recent increases in the water temperature and rainfall levels that are higher than normal," Chattanooga Public Works Administrator Justin Holland wrote in a statement. " we consider this to be a natural event outside of our control."
The fish were piled for hundreds of yards in the unnamed creek behind Memphis and Atlanta drives near Dupont Elementary. The creek pours into the Tennessee River directly across from Tennessee Riverpark.
The Tennessee Department of Environment and Conservation became aware of the issue Wednesday and notified TWRA and the city, according to a statement from agency spokeswoman Kim Schofinski. TWRA is leading the investigation, but the TDEC Division of Water Resources staff also plans to investigate.
TWRA biologist Bobby Brown was on the scene Thursday.
He determined there are two types of dead fish in and around the creek: gizzard shad and threadfin shad.
That particular type of fish is sensitive to fluctuations in water temperature, according to TVA and city officials.
A large number of shad also died at North Chickamauga Creek, according to TVA spokesman Scott Fiedler. TVA biologists said the incidents are both weather related, but they had not been to the scene near Dupont Parkway at the time of the announcement.
Several key indicators led to their assessment. The dead fish are all of the same species. TVA biologists and Tennessee Aquarium biologist Bernie Kuhajda both said that likely means the cause is not a pollutant, which would impact other types of aquatic life. Schofinski also wrote that "no obvious indications of pollution were observed."
There has also been a dramatic change in temperature and heavy rainfall in the last several weeks, which changes water temperatures and "shocks" the fish, Fiedler said.
TWRA and TDEC were not ready to determine a cause as of Thursday afternoon.
"It's just one of those things we may never know," Kuhajda said.
No one was on scene when the incident happened, so there was no one to test the water at that time, he said. If there was a bacteria or something else harmful to the fish in the water, it has likely floated away.
TWRA will continue investigating to determine the cause, the extent of the problem and find if there's civil liability.
The cause may be related to a sewage overflow from about 10 days ago, Brown said Thursday morning, but was clear it was entirely too early to determine what happened or rule out other causes.
Chattanooga's Director of Waste Resources Division Mike Patrick confirmed there was overflow during heavy rain on the weekend of Feb. 10. There is a wastewater pump station next to the creek and a sewage line and a sewer force main running through the area, he said. However, there's no indication at this point that waste overflow was the cause.