In the peak summers most of the hill stations and destinations near rivers are very crowded. I was at my in-laws in Dehradun where one of my relative told me about katapatther.
This place is about 50 km from Dehradun. It is situated off charkrata road. From chakrata road you take a narrow road which goes through mango and lichi orchids. During season you can buy fresh mango and lichi from orchids directly.
You wont find many vehicles in parking and place is less crowded. Parking charges are 40 Rs and no entry fee. As soon you enter you see a canal and besides that canal there are two water downstream coming somewhere from mountains. Site looks very scenic with vertical mountains in background and water flowing to the plains with gentle rapids. Both streams then merge to form a bigger stream and sometimes you will see excess water from canal is also released in these streams forming a artificial waterfall where you can take bath. You can spend hours in water, taking dip in canal, laying your feet in water or trying to cross water streams.
Overall its a good place to spend 4-6 hrs. Do carry drinking water and snacks with you as there are no shops around.