Nouns ending in -eau are usually masculine.
Is bateau masculine or feminine?
lebateau
The rule behind it
93.1% of -eau nouns are masculine
In context
Nous avons vu un bateau blanc au loin.
We saw a white ship far away.
Hier un bateau a coulé près d'ici.
A ship sank near here yesterday.
Le bateau se dirige droit vers le nord.
The ship is bearing due north.