It would have been easy to join friends on their gap year travels in South America or to do a ski season in the Alps, but as I love nature and enjoy scuba diving I wanted to join a marine conservation project. I chose Blue Ventures as it had a really informative website and a permanent presence in Belize and Madagascar. These were clearly proper long-term conservation projects and we were useful labour.

My parents said they would match whatever I raised towards the cost of the internship which cost about £4,500 including flights for the six-week expedition. That might sound expensive but it's very good value when you consider that a day's diving costs around £200. I took a job in a hotel to raise my half of the money.

I was a bit worried about setting off into the unknown on my own but Blue Ventures answered all my questions over health, money and safety which reassured me. I flew to Belize City and successfully caught a bus to our base, the fishing village of Sartenaga. There were 15 of us on the expedition, including the three British staff. Most of us were aged 18-25 and we all got on really well.

I wished I had made an effort to learn Spanish before I came but fortunately my American room-mate was pretty fluent and taught me the basics. I should also have read more about Belize, especially about its society and the importance of religion. That came as a surprise to me.

From our dive camp in the Bacalar Chico Marine Reserve we did four dives a day, five days a week, counting the fish on particular stretches of reef and comparing numbers to the previous year's charts. (If you can already dive, do bring your own scuba gear).

The poisonous predatory lion fish arrived on this reef six years ago, having originally escaped from an aquarium in Florida in the 1980s. They breed quickly and eat all the young fish, some of which are endangered species. It's a huge problem and one strand of this project involves showing local fishermen how to cut off the poisonous spines of the lion fish and encourage Belizeans to eat them. We ate a lot of lion fish ourselves and I can honestly say it is delicious.

I feel the trip gave me a lot more confidence. Working as part of a team was a new experience and dealing with the changing dynamics between us over the six weeks was very interesting. We all shared the chores: raking the beach, cooking, repairing the camp. Drinking isn't allowed, apart from the odd beer on a Sunday, but there was plenty to occupy us: volleyball, beach walks, birdwatching and manatee spotting.

I loved the science side of it and finding out why different fish live on particular areas of reef. By taking out the lion fish and educating people on how to prepare and eat them, I felt we were doing something practical to help preserve the local fishermen's livelihoods.

Blue Ventures (0207 697 8598; blueventures.org)

Read the rest of our gap year planning guide

Gap Year 100: our pick of the best travel firms

Gap year case study: teaching in Thailand

Gap year case study: travelling independently

Gap year case study: marine conservation in Belize

Gap year case study: teaching in Africa

Gap year case study: learning Spanish in South America

Voluntourism – who are you helping?

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