A mobile sprayer is provided for spraying through difficult terrain found in aquatic environments. The sprayer includes an amphibious vehicle equipped with a spray tank, a pump assembly connected to the spray tank, a plurality of spray nozzles, and a controller for selectively supplying fluid from the pump assembly to the spray nozzles. The sprayer has a rugged frame and boom assembly that allows multiple configurations of the sprayer to match the terrain in the environment to be sprayed. The controller is operable to individually operate multiple spray zones in each configuration of the sprayer so that any one spray zone or combination of spray zones can be covered during a spraying operation. The controller also includes a GPS receiver for providing path guidance to the sprayer, mapping of the area sprayed, and automatic adjustment of pressure at the spray nozzles based on speed for maintaining precise chemical application rates.