I think there must be a rule for watching wildlife that is something like waiting for buses. Nothing happens for hours then everything arrives at once.

We are now canoeing down the Rio Irayanez. Like every other body of water around here, it abounds with capybaras, crocodiles and pink river dolphins.

In fact, these seem to be even more plentiful here than on the lake or the Rio Yata. Pods of up to 10 dolphins follow us for hours. Maybe our paddling disturbs the piranhas and other small fish that they feed on. They seem to herd the fish. We can see three or four executing some sort of pincer movement while a couple of blockers out in front suddenly get frisky and the canoe rocks with the waves they send up. Sometimes this is quite scary.

Yesterday one blew off about a metre from my position at the front. It was heading right for us and it nearly clipped the boat with its fin as it slid underneath.

After three days riding across the pampa, we are glad to get back on to the water. We reckon on three days of hard paddling to get us to the larger Rio Mamore, one stage closer to the Brazilian border. The reality of this will be three eight-hour shifts going at it like the Moxos Indian paddlers who used to travel these waterways before the invention of aluminium launches and outboard motors. Not only are the days physically exhausting, but as the Irayanez is bordered by low scrub, not impressive rainforest, it is unshaded, very hot and at times very boring. We crave the buzz of each wildlife encounter. Seeing howler monkeys tumbling through a riverside tree raises our morale and keeps us rowing. Of course, we long to see something really special such as a jaguar that I can report back to the summer school project in Knowsley that I+m working with. Such encounters are down to luck.

Then it happens. The bus stop effect. Three days down and we+re just saying how the jungle on the banks is getting higher and more interesting. Irgen, our guide, hears Capuchin monkeys on the left side. We miss these but instead spot a group of coatis (rather like racoons) foraging on the bank.

Meanwhile the dolphins are still all around.

Then we spot something crossing the river ahead of us. We can only see its head. It’s one of those Superman moments. Is it a capybara? Is it a tapir? The possibilities narrow as it doesn’t sink or raise a trunk-like snout in the air but emerges, streaming water from its spotted coat. We savour those long moments as it pads up the bank and slips into the jungle. “El Jaguar!”

Simon Chapman is head of physics at Morecambe high school and author of the Explorers Wanted! series for children (Egmont) and The Monster of the Madidi (Aurum Press). Follow his progress for the next two weeks in The TES and keep up with the Knowsley project at www.spiritofthejaguar.org.uk