Midway across the river the outboard motor on our pirogue, as the dugout canoes in this part of Democratic Republic Congo are called, falters and dies.

These simple craft, each hewn from a single forest tree, have been paddled backwards and forwards on the Congo from time immemorial. But our motorised version, I now notice, doesn’t seem to have a paddle.

Returning to Ubundu after visiting a medical centre in the outlying village of Ndjale, we paused before climbing back into our boat to watch four young men paddling swiftly downstream to rescue a solitary boatman who had got too close to the rapids.

Now, as the gathering wind whips up little waves on the murky brown water, the already distant bank seems to be receding fast.

Our boatman tries again and again to bring the engine back to life. We drift steadily downstream.

I am sitting behind Espere Lukosa, a Congolese Ministry of Health doctor responsible for the primary healthcare of some 75,000 people - over 14,000 of them under five - in Ubundu, an area half encircled by the Congo River in Congo’s northeastern Orientale province.

Crouched in the bow in front of him is a young mother who’s begged a lift with her 10-month-old daughter, whom we gather has malarial convulsions.

While I try not to panic about the rapids, the doctor’s concern is clearly elsewhere.

He leans forward and as he lifts the baby from her mother’s arms, the blanket drops away revealing a very sick little girl. A quick look and he hands her back, but something in the way he does so makes the mother’s face crumple.

The boatman gives yet another pull on the starter, the motor splutters, and this time does not fade.

Safely back on dry land, Dr. Espere disappears up the bank with the mother and baby.