You can avoid if you want to go right now, because weather has changed, there is Thunderstorms and in this weather you would not be able to do water activities. you can wait for few days until weather is clear.
The best time to visit Rishikesh for River Rafting is from late September - October to mid November, and then the best time to visit Rishikesh is from early March - April to first week of May. In July there is a festival in Rishikesh called Savan where thousands of people flock to Rishikesh. Major roads are blocked and hotels are crowded. It is better to avoid travelling to Rishikesh during that time.