53-year-old Thomas Swindal was fishing with his brother Kenneth off the Florida Keys last Wednesday.  They found a large brick of white stuff floating in the water and guessed that it was a kilo of cocaine.

Thomas proceeded to bring it on board and stashed it with their bait.  Then they kept fishing.  But at some point, Thomas decided to TRY some.

It took about an hour and a half for Thomas to feel the effects, but when he did, he went completely DOG-NUTS.  Kenneth said he began running around the boat with sharp objects, so Kenneth threw all the knives overboard.

Then Thomas started throwing stuff overboard too, including their cell phones and the boat's radio.  That meant they couldn't call for help.  Which was a problem, since Thomas lifted the boat's ENGINE out with a hook, and threw THAT overboard too.

With no way to get help, Kenneth threw the brick overboard, climbed on top of the boat, and signaled for a rescuer.  The brothers got towed ashore, and Thomas was taken to the hospital . . . where he DIED.

Doctors are doing toxicology tests to see what Thomas snorted that caused his reaction and death.