Omringdijk already protected the north, and a high dike was constructed in the south. An 1894 source reports a mill with screw pump on the west, with the water draining into the canal which at the time also served as the outlet for the Stoomgemaal Vier Noorder Koggen, the steam-powered mill that drains the water from Aartswoud. The Kolk was recently again breached to restore wetland habitat. Meadow birds in the area include the Northern lapwing, the Black-tailed godwit, the Eurasian oystercatcher, the Great crested grebe, the Common redshank, the Common shelduck, the Black-headed gull, and the Pied avocet. The Westfriese Omringdijk runs along the Kolk, and the bicycle path between Aartswoud and Lambertschaag goes through it; there is an observation tower. The landscape evidences the entire history of the West-Frisian land, including inversieruggen (higher areas of sand in former mudflat areas), daliegaten (holes formed by the digging up of clay, which then filled up with peat that continues to sink, as opposed to the surrounding clay ground), the Omringdijk itself, and the subdivision (verkaveling) of the 17th century. While much of the area has lost its small-scale relief through levelling, old meadows of Cynosurus cristatus are still present. Those meadows are helped by the restoration of former seasonal water levels: higher in the winter, lower in the summer. Clay pits in the northern part of the area are home to Common reed and a variety of rare orchids. Part of the area has been turned into a wetland designed to mimic the tidal landscape that existed before the Omringdijk and to serve as a reservoir at high water. A creek is surrounded by wet grasslands, attracting wading birds; the area is likely to flood once every five years, and can contain 60 000 m3 (2.1 million cu ft) of water. References Notes Citations Bibliography Archaeological sites in the Netherlands Neolithic sites of Europe Nature reserves in the Netherlands Opmeer Populated places in North Holland