Lakes that have never frozen typically support different species than lakes that freeze each winter. The annual freeze-thaw cycle affects oxygen levels, nutrient mixing, and the timing of fish spawning. As warmer winters reduce ice cover in many northern lakes, biologists are documenting shifts in the species that thrive there.
Which choice best states the main idea of the text?
- A
Lakes are getting deeper.
- B
Fish spawning has stopped in northern lakes.
- Ccheck_circle
Ice cover shapes lake ecology, and warming winters are now altering northern lake species composition.
- D
Frozen lakes have less oxygen.
Explanation
The passage centers on ice's ecological role and warming-driven shifts — B. A is partial; C and D are unsupported.