We examine long-run trends in surface water quality in Texas, USA, with a focus on nutrient pollution and its potential economic impacts. Using >2 million observations of total nitrogen, total phosphorous, dissolved oxygen, and chlorophyll a concentrations from water quality monitors in the state's 23 river sub-basins, we find that nutrient pollution may be a growing problem that is essentially statewide in scope. In addition, because economic impacts of nutrient pollution depend not just on observed water quality, but also on the typical uses of surface water resources that people value, we quantify the share of the state's surface water resources that does not meet common definitions of quality suitable for boating, fishing, swimming, and drinking, as well as the share that does not meet state regulatory standards for their designated uses. This analysis indicates that water quality improvements relative to human uses have stagnated over the last three decades and that nutrient pollution represents a much greater relative threat to attainment of designated uses than it did in the 1970s. We conclude that nutrient pollution is likely taking a toll on the economic value of Texas' water resources.