The Himalayan lakes are very significant as they provide water for drinking, fishing, irrigation, recreation and tourism purposes. At present, many of these pristine lakes are under threat due to higher sedimentation, ecological degradation and pollution, especially due to human interference. The sedimentation is one of the major problems that reduces the depth and size of these lakes (Jain. 1999, 2007; Chakrapani 2002; Kumar. 2006; Das. 2008; Sarah. 2011; Mondal. 2012; Nautiyal. 2012; Chandrakiran & Kuldeep 2013; Khadka & Ramanathan 2013; Singh & Jain 2013; Bhat & Pandit 2014). The sedimentation rate in each Himalayan lake differs due to catchment lithology, slope, vegetation cover and energy of transporting media (inlet stream, rainfall and wind) causing differential erosion. The most common sediments received by the Himalayan lakes from the catchment area are gravels, sand, mud and organic matters (Rai. 2007; Choudhary. 2013). Even, the eutrophication within lakes also creates sedimentation in the form of partly decomposed organic matter (Hasler 1947).

The sedimentation rate reported from few Himalayan lakes reveals contribution of sediments due to both natural and human interference (Fort. 1989; Kusumgar. 1992; Shukla. 2002; Kumar. 2007; Rai. 2007; Choudhury. 2013). However, it is still unknown as to which one dominates. Therefore, an attempt has been made to calculate the sedimentation rate in the Rewalsar Lake, Himachal Pradesh, India and compare some of the northwestern Himalayan lakes using few common factors such as geology, slope and rainfall to delineate the anthropogenic contribution versus natural. The sedimentation rate of the Rewalsar Lake has been calculated using Pb and Cs age dating methods whereas the sedimentation records of Nainital, Bhimtal, Sattal, Naukuchiatal, Dal, Manasbal, and Mansar Lakes were acquired from the published records (Fort. 1989; Kusumgar. 1992; Shukla. 2002; Kumar. 2007; Rai. 2007; Choudhury. 2013).