Vaterpolski klub Marsonia (english: Marsonia water polo club) is a professional water polo club based in Slavonski Brod, Croatia. It was founded in 2012 with the aim of promoting, developing and improving water polo in the city and county. It was a humble beginning, full of burdens. The club gained significant momentum in the fall of 2013, when Slavonski Brod got the beautiful City Pool. “Martians”, as the nickname for the players of this club is, now they finally had everything. Their own home, swimming pool and roof over their head.

The club competes in all younger categories within the Croatian water polo association.

This club will appear at the TOMO tournament for the first time this year. Marsonia will play in the U14 category.