If it's true that every dog has its day, that day must be Aug. 11, when merchants from the Rivertown Business District have invited dogs and their owners to descend on historic downtown Antioch for an evening of four-legged fun and friendly canine competition.

Known as the "Rivertown Dog Day of Summer," the 5 to 8 p.m. event in Waldie Plaza will feature demonstrations of dog agility and obedience during the first hour, and then a non-traditional dog show begins at 6 p.m.

The offbeat dog show categories include cutest puppy, best senior dog, best dog costume, best pair of dogs, most mysterious mixed breed, and best in show (small, medium, large, extra-large). All dogs are eligible and encouraged to compete in the dog show, and there is no cost to participate.

"I grew up showing dogs, but this dog show is truly different because the average dog lover can come out with their pet and compete in a fun event that's absolutely free," said Jennifer Gallego, owner of The Garden Source and an event volunteer. "This is a unique opportunity for people who are proud of their dogs to have an experience usually reserved only for pure-breds and professional handlers."

Along with the demonstrations and dog show, nearly 20 local businesses and organizations serving the dog industry will staff booths and provide discount coupons, informational materials, brochures and other free give-aways.

Some of the businesses and organizations staffing the booths include veterinarians, groomers, pet supply companies, rescue and service organizations and the nationally recognized Guide Dogs for the Blind. Antioch Animal Services and other rescue groups will also be offering on-site adoption.

For more information and to pre-register online, go to www.art4antioch.org/dog and click on "Dog Day of Summer Registration Form." Dog show participants may also register between 5 and 5:30 p.m. on event day. But spots are limited, so those interested in competing are encouraged to register online as early as possible.

The "Rivertown Dog Day of Summer" is part of the Second Saturday series of events planned and hosted by merchants in the Rivertown Business District. A different event is planned for the second Saturday of each month through October. For more information on this and other upcoming events, e-mail bnunnally@ci.antioch.ca.us or call 779-6168.