Deep clear lakes occur in all areas of the world. The main physical parameter they share is their depth and therefore usually large water volume, which makes that these lakes only very slowly respond to eutrophication and other pollutions. Also probably because of their generally large volume and clear water, these lakes are used for all kinds of services: fishing, irrigation, recreation, drinking water etc. The environmental concern is that although these lakes seem invulnerable for (nutrient) pollutants and overfishing, they are not. Deep, clear lakes are less vulnerable for eutrophication than shallow small lakes are, however, due to continuous inflow of nutrients over the years, via rivers or rain, almost all lakes suffer to a certain extent to increasing eutrophication. Deep, clear lakes appear blue.
Within GLaSS, the following deel clear lakes have been selected: