Bij Van Assema is a marina and boat-rental facility situated on the edge of the recreational lake De Mooie Nel, within the larger Spaarnwoude recreation area between Haarlem and Amsterdam.

The marina offers around 100 berths for permanent and visiting boaters, along with storage boxes in various sizes, shore power, and water access at the visitor pontoon.

Visitors who arrive without their own vessel can rent a motorboat — no boating licence required.

From the marina, the centre of Haarlem is reachable by water in under an hour, and destinations such as Amsterdam, Zaandam, Aalsmeer, and De Kaag are within a few hours' cruising distance. A café-pavilion on site provides food and drinks.