In the once clear waters of the Caribbean, floating mats of toxic brown seaweed called sargassum blanket the water for months on end, exacerbated by the climate crisis and pollution. The result is a threat to biodiversity and livelihoods, and when it washes ashore, it emits gases harmful to human health, causing headaches, nausea and breathing problems.

This pressing, true story is the basis for choreographer Marlène Myrtil’s Océan Brun, informed by interviews with people living in Guadeloupe and Martinique, where Myrtil’s Compagnie Kaméléonite is based. This is the first time the piece has been seen outside Martinique, a move typical of the Let’s Dance International Frontiers festival in Leicester, which gives a platform to global artists every year, all from the African and African-Caribbean diaspora.

The tall stone arches of Leicester Cathedral make a stately backdrop for this duet, the daylight through its lofty windows fading over the hour to be replaced by the warm orange glow of stage lighting. The effect is a visible shifting of time, an actual change in the environment. (The downside is that in daylight, the projected film showing the sargassum-strangled sea is faint and hard to see, which is less impactful.)

The piece is like a quiet lament for the islanders’ troubles as we hear abstracted words from the local people’s testimony – “headache”, “burn”, “medicine” – while the dancers move with gasping breaths, dancing in gusts, quickly exhausting themselves (or being exhausted by their situation). There’s a sense of urgency and desperation; they raise hands to the sky in what could be a signal for help, although this dance, with its improvisatory feel, is wide open to interpretation.

Moving either in silence, to shimmering music, or to the sound of a crescendo of waves crashing, Deborah Lary and Francis Saint-Albin are fantastic performers. There is conviction and a controlled tension to everything they do – some of the choreography is influenced by the meditative movement practice of qigong. At points there is an intense, hypnotic stillness with, say, just the slightest curling of fingertips, as if they are training the viewer to really pay attention to what’s going on.