July 26: Kema River. This afternoon I nearly lose my passport in the river, prang the canoe and go for a long swim down a rapid. I also have a lot of trout soup (mainly cold and unappetising). All of this on just our first day on the river.

Before starting our main expedition down the Armu, our guide, Sergei, says we should test the canoe out on a nearby river, the Kema. It’s popular with holidaymakers from Vladivostok, who set up camps on the banks and spend their time fishing, eating what they catch, and steaming themselves in home-made tent-type saunas on the riverside shingle.

Their hospitality is overwhelming, and before we even start canoeing, we’ve been force-fed masses of trout soup, and offered a good steaming followed by a whipping down with birch branches.

Finally, we build the canoe and set off. Dippers and grey wagtails flit between the boulders sticking out of the water, and twice we see ospreys swooping for fish.

Negotiating the minor rapids adds to the thrill of being on a wilderness river. These soon increase in frequency and ferocity. Dave gets out of the canoe (he says to do some videoing, but maybe it’s because of the mounting tension over my and Sergei’s canoeing styles). He says he’ll walk back to the road and get a lift to our planned camping spot.

Five hours later, tired and less sharp than we should be on the rough water, we come to a zig-zag as the river cuts around some house-sized boulders. On the first turn the canoe ships water and the front end snags a large rock mid-stream, suddenly pitching us side-on to the flow. I jump on to the rock to stop us capsizing. Sergei nearly falls out as he too clambers up.

The canoe fills up at one end and the dry-bag containing my passport is in danger of floating off. I edge along the boulder and manage to swing the bag to safety, but I fall in and am swept along some distance before managing to get to the shore. I try to swim back across to Sergei and the canoe. The flow takes me again, but I get a fingerhold and pull myself on to the boulder. Somehow, we empty the half-sunken boat and carry on.

The rapids after that are easier, or we are more skilful at negotiating them. By then I am far too cold to care, in any case.

At least Dave and Anatoli, our driver, have hot food prepared when we arrive at the camp they’ve made. And it’s trout soup.

Simon Chapman is head of physics at Morecambe high school, Lancashire, and author of The Monster of the Madidi (Aurum Press) and the Explorers Wanted! series for children (Egmont). Throughout his expedition he will be videoconferencing with summer schools in Knowsley (www.kirkybyclc.org.ukexplorers) via satellite phone. You can follow him every week in The TES