The Rough Scientists are sent to a nearby wreck which offers a whole new artificial habitat for plants and fish. As in every programme the team are set three challenges. Firstly, Jonathan will need to design and build a submersible, remote-controlled rover to send back pictures from the sea-bed; Kathy’s challenge is to work out how to reach the wreck at low tide, when it will be most visible; while Ellen and Mike have to figure out how to purify the team’s water supply.

It’s a dark tropical night and Kate has fallen overboard and is in need of rescue. Mike has to build a distress flare, while Kathy and Ellen are tasked with making a life jacket or some sort of flotation device. Jonathan is given the job of producing a warning light that’s triggered by seawater.

The waters around Zanzibar are teeming with life and they are surprisingly noisy. The team’s challenge this week is to eavesdrop on the underwater sounds of the reef to discover what is making all the noise. Jonathan and Mike will work together to construct a hydrophone – an underwater listening device. Kathy has to build a contraption that will allow them to see under the water. Meanwhile, Ellen has to fend off some of the island’s less desirable wildlife – mosquitoes.

The team have to build a lighthouse on an outlying island which does not have electricity. Challenge one is for Ellen and Mike to make a light source that can be seen from far out at sea, while Jonathan and Kathy are challenged with building the lighthouse infrastructure and making the light flash.

This week the scientists are set their most environmentally friendly challenge yet – to protect a coral reef. The reef is home to over 400 species of tropical fish and 200 types of coral. However, it’s under threat from passing boats and the team are challenged to invent a system that can alert approaching boats that they are entering a protected area. The team come up with a quite unique solution – possibly the world’s first coral reef burglar alarm!

It’s the final challenge and perhaps the most dangerous yet. The scientists have to make a SCUBA device so that Kate can descend safely to the seabed some 5m down. It has to be sophisticated enough to supply her with breathable air at the right pressure, while giving her the freedom and time to explore beneath the waves. They only have access to the simplest tools and materials, however, and Kate has to put her trust in the team to get their Rough Science spot on this time. There can be no room for error.