To get to the island of Ometepe we have to take a ferry from Rivas, a dangerous and ugly port town all sprawled out and gently cooking on the lakeside. After a long and bumpy ride along country roads, our taxi drops us right in the danger zone – that is bang in the middle of the docks – and we are instantly swarmed while at our most vulnerable: sweaty, disoriented in the midday sun, a huge pile of bags and surfboards anchoring us down, unable to move, unsure where to go.

Tour sellers and porters pluck at my arm, men compete to sell us cheap ferry tickets, people edge forward and pick up our bags – presumably they are porters, though who knows? Money-changers wave rolls of bank notes at us. Somehow, unasked, we acquire a fixer. He hauls away our baggage into a kiosk, shoos off the beggars, marches me up to a window to buy tickets, procures us a table for lunch and paints a picture of various breathtaking excursions that he alone can organise on the island. I manage to escape without booking any expensive tours, but he extracts a $5 tip and a promise that when we return from the island he will arrange our taxi transportation onwards.

The café on the dockside looks rough and not particularly hygienic but the chicken, beans and rice they serve taste great and the tough old proprietress dusts off a cracked smile for Matilda. We pile our luggage around our table so it feels we are bunkered down in a foxhole. Occasionally an arm appears over our barricade, hand outstretched. The children judge how needy the supplicant looks, and hand over an appropriate amount of coins from a small pile that we have accumulated.

And then action! We all load up with as much luggage as each can carry and jostle our way onto the Che Guevara ferry, winding our way between hooting pickups and revving motorbikes, floating amid a sea of brown faces, jostled by old ladies with live chickens, making space for toothless men with enormous sacks of grain on their backs. We stash our surfboards and skateboards on the car deck and heave everything else up to the top floor, and there we sit triumphantly in high winds and fierce sunlight.

The passage is rough. Wind-swell rocks the ferry, white horses race us as we plough across the lake. I am seated by a huge open barrel of water that is being transported to the island and I get periodically sprayed as the boat lurches.

Lago de Nicaragua is huge – it has about the same surface area as Cyprus. It is inhabited by one of the only fresh water colonies of bull sharks in the world. These were once prolific and such savage predators that for years the lakeside inhabitants refused to learn how to swim. Now of course the sharks have been overfished to near extinction. Chinese demand for shark fins led to a booming trade back in the sixties when a hundred or so boats competed on the waters here and delivered their catch to a dedicated shark processing plant in nearby Granada. The fins went to China, the skin was used for leather, shark liver got made into supplements and the meat became dog food.

As the stock depleted this became a game of diminishing returns and the whole operation was eventually shut down after the revolution. Sharks were finally protected by law but by then over 20,000 had been killed. Nowadays there are whispers of illicit nighttime shark fishing trips, big game hunters on high speed launches – Chinese and others; corrupt officials bribed to turn a blind eye. And so it goes.

We don’t see any sharks on our journey, but there are some elegant storks that fly across our bow. We have dosed Matilda with sea sickness tablets and she flops around drowsily in the sun. The crossing lasts for forty minutes and then we are on the volcanic island of Ometepe. A pickup truck sits waiting for us at the dockside and once we have loaded the baggage, and our son, into the rear, we roll slowly across the island, down roads lined with lush shiny-green foliage, into little rural villages, through coffee plantations and up steep hills. Then at last the day’s journey is complete and we are at Tenorio Lodge.

We rest. Tomorrow we climb the volcano.