A U-shaped lake formed when a river meander is cut off is an ____.

• A. Playa Lake
• B. Reservoir
• C. Oxbow Lake
• D. Lake

Answer: (C)

A lake that forms when a river’s loop is cut off is an oxbow lake. The idea is that a meandering river erodes the outer bend and deposits on the inner bend, creating a loop that becomes narrowed at the neck. When floodwaters break through the neck, the river short-circuits the loop and takes a straighter course, leaving the old bend isolated from the main channel. Water then fills that abandoned bend, creating a crescent- or U-shaped lake that often sits near the old meander.

This is different from a playa lake, which forms in arid regions as a temporary reservoir in a desert basin; a reservoir is a man-made lake created by damming a river; and a generic lake is simply any natural body of water without specifying this meander-cutoff origin.