Both Starflight and Austin Fire joined the search efforts on the water to attempt to locate the person and animal.
A drone was also launched to search for them.
ATCEMS canceled the rescue effort around 3 p.m. after an extensive search resulted in no one being located. Witnesses said someone had exited the river, and a dog was seen on the trail. No one is believed to be in danger as of now, ATCEMS says.