"Ice Tea Party" is a side mission in Infamous 2.
The mission starts when a civilian approaches Cole and informs him that Icemen have commandeered several Militia supply ships, and that the Militia are fighting back. Cole must then find the battlefield and join the fight and knock all of the supplies off the boats. The mission is complete when all of the supplies have been either destroyed or thrown into the water.
Use Cole's shockwave to knock all of the supplies off the boats. Killing the enemies is optional, but you will gain extra experience points if you do. Use Cole's grenades to destroy the enemy boat, then shock the water to make sure they are dead.