Kanwad/kanwar mela is celebrated in month of July/August. In this thousands of devotees from all over north india come to the city of haridwar to collect the holy water of Ganga.
During Kanwar Mela, pilgrims come to collect Ganga water to offer it to Lord Shiva.
Most of them come, collect water and go. They do not stay in Rishikesh as they often travel 100s of miles on foot to their places.
Just one thing, during Kanwar, Rishikesh/Haridwar remain very crowded. At this time going to any place from Rishikesh by road is not possible. Train Travel is the only possibility.