ABSTRACT The ef‘ciency of hot water spray to decontaminate boats exposed to quagga mussels was evaluated in the ‘eld. The water temperature and exposure time needed to result in complete mortality were determined. The time needed for three types of boat areas (easy access, hard access, and specializedareas [i.e., bait and live wells]) to reach the lethal temperature for the required exposure time was determined. Field validation tests were conducted in the summer and winter for the easy access and hard access areas. Summer tests of both areas resulted in 100% mortality, while seven out of eight winter tests resulted in 100% mortality. For bait and live wells, the time needed to reach lethal temperature in winter was much longer than in summer time.