De Eerste Aanleg is a marina and water-sports access point situated on the Loosdrechtse Plassen near Breukelen, in one of the most celebrated watersports regions of central Netherlands.

The harbour sits in a wave-free position with an open connection to the Loosdrechtse Plassen and the Vecht, and borders the Kievietsbuurt nature reserve.

The marina accommodates around 150 boats and several houseboats, with seasonal and transient moorings available. Visitors can rent sloops, motorboats, canoes, or SUP boards to explore the surrounding lakes and waterways.

Swimming and fishing from the shore are also possible, with day fishing permits on offer. Boat maintenance, repairs, and both summer and winter storage round out the facilities.