Aquarist Atlas
Water character

Crater lake

Crater lakes fill the calderas and explosion craters of volcanoes — small, often startlingly deep bowls of water walled off from the river networks around them. The atlas holds two famous pairs: Barombi Mbo and Bermin on the Cameroon volcanic line, and Apoyo and Xiloá on Nicaragua's chain of maars.

A crater lake is born isolated. Ringed by its own walls, it typically has no large river in or out; rain and groundwater fill it, and its chemistry is set by the local volcanic rock rather than by the surrounding basin. That is why Nicaragua's crater lakes differ so sharply from the great lakes a few kilometres away — Barlow and colleagues' 1976 survey found each crater carrying its own distinct water, from moderately mineral to brackish-hard.

They are deep for their size, warm, and often stably stratified, with oxygen confined to the upper water — Barombi Mbo's depths are anoxic, and the Cameroon line carries the darker hazard of gas-charged deep water, of which the 1986 Lake Nyos disaster is the extreme case. Shorelines drop away fast, so the living habitat is a narrow, sunlit rim around a deep centre.

Their isolation made them evolution's showcases. A closed bowl with no escape is a natural laboratory, and crater lakes supplied the textbook cases of sympatric speciation — new species arising side by side with nowhere to go: Barombi Mbo's endemic tilapias and the Midas cichlid flocks of Apoyo and Xiloá. The same isolation cuts the other way: a species whose entire world is one small crater is among the most extinction-prone fish anywhere.

Waters of this character in the atlas (4)

West-Central AfricaBarombi Mbo →11 endemic cichlid speciesCentral AmericaLaguna de Apoyo →~6 endemic (Midas flock) cichlid speciesCentral AmericaLaguna de Xiloá →~9 total (4 endemic Amphilophus) cichlid speciesWest-Central AfricaLake Bermin →9 endemic (Coptodon flock) cichlid species

Sources

  1. Chemical Analyses of some Crater Lakes in Relation to Adjacent Lake Nicaragua (Barlow, Baylis & Roberts, 1976) — Lake Jiloá temperature, oxygen, pH, conductivity & ion chemistry profiles
  2. Comparative transparency, depth of mixing, and stability of stratification in lakes of Cameroon (Kling, Limnology & Oceanography, 1988) — Barombi Mbo morphometry, temperature, oxygen, Secchi, conductivity
  3. Sympatric speciation suggested by monophyly of crater lake cichlids (Schliewen, Tautz & Pääbo, Nature, 1994)
  4. Incipient sympatric speciation in Midas cichlid fish from the youngest and one of the smallest crater lakes in Nicaragua (benthic/limnetic ecomorphs)
  5. The 1986 Lake Nyos gas disaster, Cameroon (USGS Open-File Report) — limnic eruptions on the Cameroon Volcanic Line
How to cite

Aquarist Atlas (2026). Crater lake — water character. Aquarist Atlas. https://www.aquaristatlas.com/water/type/crater-lake/