The tourism-dominated watershed area in North Goa, India has a contiguous stretch of marine water bodies - the open sea between Sinquerim and Chapora; the three estuaries of rivers Chapora, Mandovi, and Nerul; and a small stream under tidal influence at Baga. The present study involving seasonal (pre-monsoon, monsoon, and post-monsoon) monitoring does not show any polluting influence of tourism-related activities on these water bodies. A marked increase in values of BOD (biochemical oxygen demand) was observed at certain stations during the main fair-weather (post-monsoon) sampling period, but these occurrences appear to be due to some episodic release of biodegradable organic matter in the marine environment. Such high values of BOD did not recur during the monsoon and pre-monsoon samplings at these or other stations. The marine waters all over the sampling sites are very well oxygenated at all the seasonal observations. This chapter also contains a section on grading of the water quality criteria to indicate the levels of pollution of a water body, based on the classification method of the Central Pollution Controlled Board of India