Great News from Lake Mývatn: Unique marimo colonies grow second year in a row

The ecosystem of lake Mývatn appears to have continued to recover this past summer. Biologists and locals have noted that the unique marimo colonies in the lake have expanded. The small lake midges, the Chironomidae which are a key food for all animal life at the lake, have been doing well this summer. This is the second year in a row the ecosystem of Mývatn has shown sings of improvement.


Read more: Unexpected good news from lake Mývatn: Large quantities of Marimo wash ashore

A biologist with the Natural History Institute in North Iceland told the local newspaper Morgunblaðið that the algae growth which forms marimo has been expanding this summer. Most of the growth is still too small to generate the lake balls which are also known as marimo ("kúluskítur" in Icelandic), but small marimo balls have been found in growing numbers. Marimo had all but disappeared from the lake, causing serious concern.

Cyanobacteria blooms which have been growing in recent years, due to organic pollution from faulty and inadequate sewage systems in the surrounding settlements, have both stopped sunlight from reaching the lake bottom, where the marimo grows, and deprived the water of oxygen. The reason for the positive bounce-back of the ecosystem and the marimo in the past two years is that the cyanobacteria blooms have formed later in summer than previously.

Marimo, known as "muck balls" in Icelandic (kúluskítur) marimo was once extremely common in Mývatn. Mývatn is one of only a handful of lakes in the world which have large marimo colonies. The other major marimo colonies are found in Lake Akan in Japan, while smaller colonies have been found in lakes in Siberia, Estonia, Scotland and Iceland.