Mario Gonzales, Rick Kent and Steve Brown, shown here above Lake Marble Falls, are teaming up to present the Ultra 520K Texas in September.

When a long-distance open-water swim, a full marathon (or two), and an all-day bike race through the Texas Hill Country (or three) just arent enough, its time to register for the Ultra 520K Texas.

Organizers announced details this week of the grueling new individual endurance event, scheduled to take place in Marble Falls Sept. 25-27. The race will feature three day-long stages covering a total of 520 kilometers, or 323 miles.

Stage One is a 10K out and back swim in Lake Marble Falls, followed by a 90-mile bike loop to Llano, Burnet and back. Stage Two is a 172-mile bike loop south and southwest of Marble Falls, plotted out by Fred Boethling, race director of the Race Across America. Stage Three is a hilly, out and back double marathon.

Overall finish time will be based on the combined times from all three stages.

Participation is by invitation only, with a maximum of 35 athletes. Applicants must have finished an Iron distance event in the previous 18 months in less than 14 hours and 30 minutes.

Apply on line here. Entry fee is $1,800.

Marble Falls, by the way, is turning into a mecca for endurance events. The RAAM Challenge, a long-distance bike race hosted by the folks who put on Race Across America, just wrapped a few weeks ago. The Hill Country Marathon takes place there each fall, and this weekend the city hosts the HITS Triathlon Series.

Marble Falls is about an hour northwest of Austin on Highway 71.

Austin photographer and former endurance athlete Rick Kent is teaming with Steve Brown, race director of Ultra 520K Canada and race director Mario Gonzales to put on the new event.

Im very excited to have Kent and his organization in Texas become the first Ultra 520K outside Canada, Brown said in a press release. We anticipate a long and mutually beneficial relationship for Ultra 520K.