What does the cryptic crossword clue "Mastered swimming in groups according to ability (8)" mean?

The definition is "ability". The wordplay uses an anagram. anagram of MASTERED = STREAMED; definition: "ability" The answer is STREAMED.

Mastered swimming in groups according to ability (8)

Independent Cryptic #1807 | 9 Across | 2024-10-13 flower