While some online say it’s just kids having fun, police in Brentwood and Alameda warn that planned teen gatherings and an ‘assassin’ water gun game circulating on social media could turn dangerous.

The Alameda Police Department said it is monitoring two unpermitted beach parties advertised on social media for Sunday and Tuesday at Crown Beach, an East Bay Regional Park District property, as well as an “assassin-style” game circulating online — a concern Brentwood police also flagged last week. Alameda police, who said there will be increased police presence on both days, said the gatherings raise concerns “regarding the safety and supervision of minors.”

The game involves water guns and balloons, with players trying to eliminate each other, and has long been played by high schoolers.

But police say recent versions across the country have taken dangerous turns, with participants running through neighborhoods in camouflage or all-black clothing, jumping in and out of vehicles, conducting “drive-by” water gun shootings in parking lots and carrying toy firearms that can look real.

“From a distance, officers and community members cannot always distinguish between a toy and a real firearm, which creates a potentially dangerous situation for everyone involved,” Brentwood police said.

Alameda police echoed the concern.

“While this may seem like harmless fun, similar games in the past have led to unintended and dangerous consequences,” the department said in a Facebook post.

Both cities have responded to similar chaotic teen gatherings on the same day last summer.

In July 2025, about 300 people — mostly minors — swarmed the Streets of Brentwood mall, with several fights breaking out. In Alameda, hundreds of youths gathered at the South Shore Center parking lot, where police reported fights and two people were hospitalized.

Reaction on social media was mixed, with some defending the gatherings as kids having fun and others raising concerns about safety.

Police reminded the public that toy or imitation weapons are not allowed on school campuses, and that trespassing, reckless driving or suspicious activity could result in citations. Parents may also be financially liable for damages or injuries tied to their child’s participation.

Brentwood police urged residents to report suspicious activity to law enforcement.