Bos van Aa

Bos van Aa is a nature reserve in Zemst-Laar, a district of the municipality of Zemst in the Flemish Brabant province of Belgium. It lies close to the Brussels–Scheldt Canal, a few kilometers southeast of Kapelle-op-den-Bos, on land owned by the waterway authority Waterwegen en Zeekanaal.

Where does the name come from and how has the site changed over time?

The name "Bos van Aa" already appears in historical records from the 14th century, when the forested area covered roughly 400 bunder — about 500 hectares. Over the following centuries the land repeatedly changed character: the extensive forest gave way to farmland, and over the past century it underwent an even more dramatic transformation, as its grasslands were turned into an intensively worked industrial sand quarry. Sand extraction left behind depressions and pools that, over time, were reclaimed by vegetation and wildlife.

Why is the site protected today?

After quarrying ended, the terrain spontaneously developed into an exceptional nature area with remarkable biodiversity. Bos van Aa is now a nature reserve protected both nationally and internationally: it forms part of the Natura 2000 network, within the site "Forests of the southeast of the Zandleemstreek" (designated BE2300044). Protection covers the woodland itself as well as the wetlands and open water bodies that emerged from the former quarry.

What can visitors see here?

A mosaic of habitats — woodland, former quarry pools, wet meadows, and marshy ground — makes Bos van Aa a genuine haven for wildlife. The site is known for its rich populations of butterflies and dragonflies, as well as abundant waterfowl and wading birds. This ecological diversity draws both researchers and nature lovers looking for a quiet place to walk among varied landscapes.

Bos van Aa also carries considerable geological and paleontological significance. Fossil material from the Ice Age has been uncovered in the former sand quarry, including remains of woolly mammoths, giant Irish deer, and woolly rhinoceroses. These finds are displayed at a local museum, Het Bos Van Aa Museum, which explains the site's geological and paleontological history and how the former sand pit turned into a nature reserve.

Who manages the site?

Nature management of the area, which also extends to the neighboring Kollintenbos, is carried out by the local branch of the conservation organization Natuurpunt (Natuurpunt Zemst). Part of the reserve functions as a bee sanctuary, supporting wild bees and other pollinating insects. The municipality of Zemst also organizes seasonal guided walks through the forest, including a summer edition where visitors can learn about the site's history and its wildlife up close.

Frequently asked questions

Where exactly is Bos van Aa located? In Zemst-Laar, within the municipality of Zemst, Flemish Brabant province, near the Brussels–Scheldt Canal and a few kilometers from Kapelle-op-den-Bos.

Is it a natural forest or a site shaped by human activity? Historically it was forest dating back to the 14th century, later converted to farmland, and then transformed into an industrial sand quarry. Today's natural landscape largely developed on its own after quarrying stopped.

What makes the site especially notable? Ice Age fossils — woolly mammoths, giant Irish deer, and woolly rhinoceroses — displayed at a local museum, along with rich populations of butterflies, dragonflies, and waterfowl.

Is the area protected? Yes, as part of the Natura 2000 network (site BE2300044) and as a nationally recognized nature reserve.

Can it be visited with a guide? Yes, the municipality of Zemst organizes seasonal guided walks through Bos van Aa.