A method of treating an agricultural-water canal to decompose organic debris in the agricultural-water canal provides a controlled delivery of calcium hypochlorite particles to the surface of water by entraining calcium hypochlorite particles in an air stream and then propelling the calcium hypochlorite-laden air stream at high velocity to the surface of the water, whereat the calcium hypochlorite particles are released from the air stream. A device for implementing the method is also disclosed. The device includes a gas blower, a feed hopper and a port which is adapted to direct and propel the biocide-laden gaseous stream to the surface of water in the agricultural-water canal.