*Update 10/3* Austin/Travis County EMS reports that a dive team has recovered the body of the victim.
The Austin-Travis County EMS and STAR Flight are responding to reports of a male in his twenties who did not resurface in Hamilton Pool. Hamilton Pool Preserve currently allows swimming but there is no lifeguard on duty.
According to ATCEMS, park staff reported a swimmer in the water who failed to resurface. Austin - Travis County EMS also reported that they were unable to locate him. Rescue efforts have now been terminated.
The incident has transitioned into recovery mode.
According to Lake Travis Fire Rescue, the missing swimmer is an 18 to 25 year old male.
The swimmer was with friends at the park this afternoon. Witnesses told first responders that the swimmer was obviously in distress before he went under. Authorities haven't determined what factors played into the possible drowning at this point.
"The water in the area of Hamilton pool where this individual was last seen is about 15-20 feet deep it's generally a pretty easy body of water to see through but because there were so many people out on such a beautiful day the silt had been kicked up so visibility isn't quite as good as it usually is," said Kristen Dark with the Travis County Sheriff's Office.
The park is currently closed to visitors and will remain that way tomorrow and until the man is located.
A dive team with the Austin Police Department will resume their search of the pool around noon tomorrow.
Hamilton Pool Preserve is a historic swimming hole. Hamilton Creek spills out over limestone outcroppings to create a 50 foot waterfall as it plunges into the head of a steep box canyon. Beginning on May 15, 2016, reservations became required to enter Hamilton Pool Preserve.
This is a developing story and will be updated with more information as it becomes available.