Editing Marimo (section)

===Population decline===
The species is sensitive to the amount of nutrients in the water. An [[Eutrophication|excess of nutrients]] (due to agriculture and [[fish farming]]), along with mud deposition from human activity are thought to be the main causes for its disappearance from many lakes.<ref name="population-decline" />

The species still exists in [[Lake Zell]] in Austria (where it was first discovered in the 1820s) but the lake ball growth form has not been found there since around 1910. The same has happened in most locations in England and Scotland, where mainly the attached form can be found.<ref name="population-decline" />
[[File:Mývatn-pjt.jpg|thumb|320x320px|[[Mývatn|Lake Mývatn]] in Iceland.]]
Dense colonies of marimo were discovered in [[Mývatn|Lake Mývatn]] in Iceland in 1978, but they have shrunk considerably since then. By 2014 the marimo had almost completely disappeared from the lake due to an excess of nutrients.<ref>{{Cite news|url=https://www.mbl.is/frettir/innlent/2014/05/02/einkenni_myvatns_ad_hverfa/|title=Einkenni Mývatns að hverfa|date=2014-05-02|work=[[Morgunblaðið]]|language=is}}</ref> The ecosystem is now improving and small marimo balls are forming again.<ref>{{Cite web|url=https://icelandmag.is/article/unexpected-good-news-lake-myvatn-large-quantities-marimo-wash-ashore|title=Unexpected good news from lake Mývatn: Large quantities of Marimo wash ashore|website=Icelandmag}}</ref><ref>{{Cite web|url=https://icelandmag.is/article/great-news-myvatn-lake-unique-marimo-colonies-grow-second-year-a-row|title=Great news from Mývatn lake: Unique marimo colonies grow second year in a row|website=Icelandmag}}</ref>

The species can still be found in several places in Japan, but populations have also declined there.<ref name="population-decline" /> At Lake Akan, a great effort is spent on the conservation of the lake balls.

The marimo has been a [[Conservation status|protected species]] in Japan since the 1920s, and in Iceland since 2006. Lake Akan is protected as a [[national park]] and Lake Mývatn is protected as a [[nature reserve]].