As I leave the Environment Ministry I can’t help feeling a little deflated.

I had been looking forward to a good confrontational interview but I have to concede that the minister’s position is reasonable - it is too early to judge the government’s record.

Nevertheless, given the state of the river and history of efforts to improve it, it is hard to be optimistic.

It takes something very special to give me any sense of optimism about the Ganges.

This begins with a tantalising invitation from contacts at the WWF, who ask if I want to try to get a glimpse one of the rarest species in India, the Ganges river dolphin.

These extraordinary animals are to all intents and purposes blind - they have evolved a system of echolocation to navigate and catch fish in the murky waters of the Ganges.

But they are threatened with extinction. Back in the 1980s the population was reckoned to have fallen to just 5,000 in India.

According to a recent survey by WWF there are now fewer than 2,000 left, and that figure is higher than the experts were expecting.

When I mention my dolphin-watching ambitions to a grizzled fellow journalist over a large Black Dog whisky at the picturesquely decrepit foreign correspondents’ club in the centre of Delhi, he meets them with a derisive snort.

“Not only are they very rare, but they aren’t nearly as frisky as their maritime cousins,” he warns. “You’ll be lucky to see anything more than a grey dorsal fin break the surface.”

My hopes suitably quashed, I await further details from WWF.

I’m expecting that we’ll be heading to the higher reaches of the river where the water is cleanest but they tell me to meet them in Allahabad.

The city is on one of the most polluted stretches of the Ganges of them all, just downstream from Kanpur.

With a camera crew, I drive to a little village. We have been told to get there by 10:00 because the dolphins are most active in the morning.

I’m prepared for a long wait, but as I walk down a steep slope on to the sandy banks beside the river I see something break the surface.