The most common and most likely answer to this crossword clue is the 6 letter word EIGHTS
I've seen this crossword clue in The Daily Telegraph
E
I
G
H
T
S
Buddy explains!

The straight part
We know that "rowing race" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rowing race = eights.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EIGHTS mean?
EIGHTS noun- An island in a river, especially the River Thames in England.
- The digit/figure 8.
- Any of the four cards in a normal deck with the value eight.
- A light, narrow rowing boat, especially one used in competitive rowing, steered by a cox, in which eight rowers each have two oars.
- (especially in plural) A race in which such craft participate.
- The eight people who crew a rowing-boat.
- A pair of eights.