What does the cryptic crossword clue "Reason for drop in level of eg a lake possibly (7)" mean?

The wordplay uses an anagram. anagram of EG + A + LAKE = LEAKAGE The answer is LEAKAGE.

Reason for drop in level of eg a lake possibly (7)

Daily Mail Cryptic #16630 | 28 Across | 2021-07-29 flower