The Tirthan rises in the Great Himalayan National Park and runs about seventy kilometres to the Beas at Larji, without a single dam on the way.

Its brown trout, first stocked more than a century ago, draw anglers from across the country. Fishing is by permit only, with a limit on the catch.

Villagers along the river have formed watch groups to stop fishing with nets and explosives, which still happens in the lean months.

Guesthouse owners in the valley say the clear water is the reason their guests come. They worry about the new buildings going up close to the bank.