What does the cryptic crossword clue "Cause of 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.

Cause of drop in level of eg a lake possibly? (7)

Daily Mail Cryptic #16382 | 27 Across | 2020-08-17 flower