It was a perfect morning in Pigeon Island National Park in eastern Sri Lanka, where a group of tourists in a boat was taking in the rich marine life in the water around them. All of a sudden, there was a loud blast close by. As silence settled once again, they saw the fish that had been flitting nimbly about now either floating dead on the surface or struggling to swim. Through the clear water, they could see more dead fish in the seabed.