What does the cryptic crossword clue "Small body of water, and reducing in size? (4,3)" mean?

The wordplay uses a container (one word inside another). ALS (synonym="ALS") in AREA (synonym="size") = ARALSEA The answer is ARALSEA.

Small body of water, and reducing in size? (4,3)

Guardian Cryptic #29353 | 22 Across | 2024-04-10 flower