An all-out brawl broke out at a Florida lake -- and it was so brutal that two people were knocked unconscious before police rounded up the suspects and tossed them in the pokey!

The donnybrook, which kicked off August 2, was captured on cellphone video by a witness at Lake Winterset in Polk County -- about an hour east of Tampa -- and later uploaded to social media.

Check out the footage ... the knuckleheads went all WWE for the camera, throwing punches and kicking each other. One dude is seen lying unconscious on the ground as a young bikini-clad woman performs CPR on him.

Making matters worse, police say several minors were subjected to all the violence. One person even told cops that his family outing was completely ruined by the melee because it caused his loved ones distress. Ga

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