The Marnix has two large swimming pools; a competition pool measuring 25 x 12.5 metres and a heated instruction pool measuring 20 x 10 metres. The water level of the pools is the same as the water level of the nearby canal, which can be seen from inside the baths which gives the impression of swimming in open water amongst the boats and the ducks.
Both pools incorporate the latest technical inventions, such as a massage-lane, an adjustable floor, an electronic lifeguard-system and a special disinfection system. The pools have, in addition to the standard filters, an OZON installation. This means that less participles of chlorine are being released into the water. Instead, the installation releases an environmental-friendly salt-solution, which benefits the swimmers, who suffer less from a chlorine-smell or tingly eyes.