I have a buddy who is pretty hardcore into lasers.

"Pretty Hardcore" might be an understatement.

I asked him what he thought and he said that if the aquarium has water, that the water will dissipate the heat and prevent it from burning the critters.

We was also surprised that it wouldn't burn a paper towel.

In his words "3 Watt is pretty powerful, how much did he pay for that?"

This is a from a guy who frequently pops balloons with his lasers whenever there is a party in our office.

Update: I was surprised that it didn't burn the paper towel.

My friend was NOT surprised as the white of a paper towel will just reflect the laser, because the color white is good at that.

Apparently the color of the object and the color of the laser have a lot to do with what you can burn.