The Vakhsh River, from the Qurghonteppa airport downstream to the bridge at Qizilqala, has some great grass and rock beaches. You will need a car or a bicycle to get from Qurghonteppa City to the Vakhsh River, so there are usually only a few people swimming and picnicking.
Is the Vakhsh River dangerous? If you try to swim in the main channel you will be taken downstream in a very strong current. But you should be OK if you stay in the smaller side channels.
Outside of the warm season, the Vakhsh River rock beaches are still nice to visit. This photo below was taken on a sunny day in February.
If you like rock collecting, the Vakhsh River is amazing. Here are some examples:
Exact map locations and directions coming soon.