Improved water clarity is associated with increased numbers of recreational visits to lakes in Minnesota and Iowa. People were willing to travel 56 minutes farther for every one-meter increase in water clarity based on this analysis of geotagged Flickr photos and water quality data.
Keeler, Bonnie L., Spencer A. Wood, Stephen Polasky, Catherine Kling, Christopher T. Filstrup, and John A. Downing. (2015). Recreational demand for clean water: evidence from geotagged photographs by visitors to lakes. Frontiers in Ecology and the Environment 13(2), 76-81.