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1. This report presents information resulting from a survey of the limnology of the 20 major lakes and tarns in the English Lake District based on samples taken in January, April, July and October 2010. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000 and 2005. 2. On each sampling occasion depth-profiles were collected of water temperature and oxygen concentration and Secchi depth was measured. An integrated water sample was analysed for pH and alkalinity, major cations and anions, plant nutrients, phytoplankton chlorophyll a and species composition and zooplankton abundance and species composition. Some of the field work and chemical analyses were carried out collaboratively between staff from CEH and the Environment Agency. 3. The lakes had a range in tendency to stratify in summer with the weakest stratification in large, relatively shallow and exposed lakes such as Bassenthwaite Lake. During summer stratification oxygen-depletion at depth was only found in the more productive lakes. 4. Water clarity, assessed by Secchi disc, varied between about 13 m in clear unproductive lakes such as Wastwater to less than 2 m in the more productive lakes during summer such as Esthwaite Water. 5. Major ion composition varied with geology and altitude. Lakes on the Silurian slates (those in the Windermere and Coniston Water catchments) tended to have anions dominated by alkalinity (bicarbonate) and cations dominated by calcium whereas the other lakes tended to have anions dominated by chloride and cations dominated by sodium. 6. Availability of phosphorus is the main factor that affects lake productivity. Concentrations were lowest in Wastwater and Ennerdale Water and highest in Elterwater and Esthwaite Water. Nitrate was the dominant form of nitrogen. Nitrate concentrations tended to be lowest in July because of biological uptake and seasonal fluctuations were most marked in the productive lakes. Silica, an essential nutrient for diatoms, showed a similar

1. This report presents information resulting from a survey of the limnology of the 20 major lakes and tarns in the English Lake District based on samples taken in January, April, July and October 2010. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000 and 2005. 2. On each sampling occasion depth-profiles were collected of water temperature and oxygen concentration and Secchi depth was measured. An integrated water sample was analysed for pH and alkalinity, major cations and anions, plant nutrients, phytoplankton chlorophyll a and species composition and zooplankton abundance and species composition. Some of the field work and chemical analyses were carried out collaboratively between staff from CEH and the Environment Agency. 3. The lakes had a range in tendency to stratify in summer with the weakest stratification in large, relatively shallow and exposed lakes such as Bassenthwaite Lake. During summer stratification oxygen-depletion at depth was only found in the more productive lakes. 4. Water clarity, assessed by Secchi disc, varied between about 13 m in clear unproductive lakes such as Wastwater to less than 2 m in the more productive lakes during summer such as Esthwaite Water. 5. Major ion composition varied with geology and altitude. Lakes on the Silurian slates (those in the Windermere and Coniston Water catchments) tended to have anions dominated by alkalinity (bicarbonate) and cations dominated by calcium whereas the other lakes tended to have anions dominated by chloride and cations dominated by sodium. 6. Availability of phosphorus is the main factor that affects lake productivity. Concentrations were lowest in Wastwater and Ennerdale Water and highest in Elterwater and Esthwaite Water. Nitrate was the dominant form of nitrogen. Nitrate concentrations tended to be lowest in July because of biological uptake and seasonal fluctuations were most marked in the productive lakes. Silica, an essential nutrient for diatoms, showed a similar