Why can phytoplankton survive only in the euphotic zone of a lake?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

lake Lake Ann in North Cascades National Park, Washington, U.S., viewed from the park's Maple Loop Trail. The North Cascades National Park is a large wilderness area that preserves majestic mountain scenery, snowfields, glaciers, and other unique natural features.

Phytoplankton can survive in the euphotic zone of a lake because it is the region where sunlight is sufficient to support photosynthesis.1

In a lake, the availability of light decreases with depth, and there exists a specific point known as the compensation depth. At this depth, the energy produced by photosynthesis is exactly matched by the energy lost through respiration. The euphotic zone is the area above this compensation depth where light levels are high enough to allow for a net gain in energy, enabling phytoplankton to thrive.1

Below this zone lies the aphotic zone, where light is insufficient for photosynthetic production. Consequently, phytoplankton cannot survive in these deeper waters unless they are capable of vertical migration.1