Thomas Lazar / Two Coyotes {Canis latrans} fighting on frozen pond, Kettle River, Minnesota, USA, winter

Yva Momatiuk & John Eastcott / Glacial kettle pond with Alaska Range and Mount McKinley in distance, Denali National Park and Preserve, Alaska

Yva Momatiuk & John Eastcott / American Beaver (Castor canadensis) young animal munching on alder branches in glacial kettle pond, Denali National Park and Preserve, Alaska

Yva Momatiuk & John Eastcott / Alaska Moose (Alces alces gigas) bull with water dripping from antlers after feeding in glacial kettle pond, Denali National Park and Preserve, Alaska

Yva Momatiuk & John Eastcott / Alaska Moose (Alces alces gigas) bull submerges head and antlers while feeding on bottom of glacial kettle pond, Denali National Park and Preserve, Alaska

Will Watson / Electro-fishing a glacial kettle hole pond, Kenchester, Herefordshire, England, March.

Will Watson / Kettle hole pool which is aquifer-fed pool with fluctuating water levels, with Soft hornwort (Ceratophyllum submersum), Herefordshire. UK, July 2013.

Will Watson / Glacial kettle hole pond with fringe of Common Spike-rush (Eleochatris palustris) Kenchester, Herefordshire, UK, July 2013.

Will Watson / Glacial kettle hole pond with Credenhill Hill-fort in background, at Kenchester, Herefordshire, UK, July 2013.

Will Watson / Yellow-green alga (Botrydium granulatum) on margin of glacial kettle-hole pond, Herefordshire, England, UK, October

Will Watson / Yellow-green alga (Botrydium granulatum) on margin of glacial kettle-hole pond, Herefordshire, England, UK, October

Will Watson / Reflections of Grey willow (Salix cinerea) and Alder (Alnus glutinosa) trees, with exposed dead wood in a glacial kettle hole pond, Herefordshire, England, UK, Europe, November