(Josh Reynolds for The Boston Globe)
Hundreds of people will drench each other on Saturday at the Banditos Misteriosos Water Gun Battle.
The soaking showdown will begin at 2 p.m. but the location, which has so far been undisclosed, will be announced on the organizers' website at midnight.
This year's theme, "See Something, Spray Something," is based on the MBTA.
People can register ahead of time to sign up for teams based on four color-coded MBTA lines. Participants are encouraged to dress up in T-related costumes.
More than 400 participants have registered, though many will register at the last minute, according to spokesman "Bandito S," who declined to give his real name.
The group predicted that the Red Line and Green Line teams would be most popular and had to close out that registration option for a period of time to even out the teams. "But we've found out that people are picking teams based on what color shirt they have available to wear that day," he said.
Some creative costumes to expect this year include a horse head costume to represent Suffolk Downs on the Blue Line and a Jackie O costume for the JFK stop on the Red Line, said "Bandito S."
The Banditos Misteriosos holds frequent events across the area, like the 2012 Pillow Fight in the North End Park. Organizers said they try to hold events that are open to everyone in the public and organized for the fun of participants involved.
Last year's theme was between two teams, the Swamp Creatures vs. the Revere Horse Men. The battle was held at the Esplanade, with some creating their own plastic shields or improvised water bottles as weapons.
The event usually lasts for a half hour-- about the time the water reserves are depleted.