The plight of Mýnvatn’s disappearing marimo can be directly traced to human activity.
Fréttablaðið reports that for the past two summers, definitive signs have been shown that Lake Mývatn is being beset with eutrophication, wherein nutrient-rich run-off from agricultural production pollutes the water.
Árni Einarsson, the director of the Nature Research Institute, told reports that high levels of nitrogen and phosphorus have been detected in the water. These nutrients feed bacteria, leading to a growth boom, which effectively blocks the sunlight that the marimo on the lake bottom need. These pollutants are, Árni said, a direct result of human activity in the region.
Marimo populations in Japan were also once threatened by exactly the same problem, but managed to restore marimo numbers by diverting argicultural and other waste water run-off away from areas where they grow.
Human influence on the lake has been a matter of public record for some time now, and marimo numbers have declined drastically. There may still be hope to bring the marimo back to previous numbers, but this would have to entail somehow reducing the amount of run-off that makes its way into the lake.