By Marilyn Haigh

BRUSSELS (Reuters) - Belgium is about to get smaller and the Netherlands bigger.

The two countries have agreed to a swap of land, a peaceful handover on a continent where borders have long been a source of bloodshed.

Each will cede small, uninhabited parcels of land to reflect a change in course of what is known in French as the river Meuse, and in Dutch as the Maas.

But it is not equal. Belgium will give two peninsulas of 16 hectares (40 acres) to the Netherlands and receive one of 3 hectares in return.

It all comes down to humans messing with Mother Nature, in this case straightening the river.

After Belgium gained independence from the Netherlands in 1830, the border was drawn along the Meuse. But in 1961, the river was straightened to make navigation easier, placing parts of each country's territory on the other side of the river.

With the current border, the only way to reach the land without crossing into another country is by boat.

A Belgian foreign ministry spokesman said police would find it very difficult to access the strips of land that Belgium is relinquishing if any incident were to occur.

"It was just not logical that that small piece was still part of Belgium," he said.

The border will most likely change at the start of 2018 after both countries have ratified a treaty signed on Monday by the Dutch and Belgian foreign ministers.

The land swap, however, does not extend to the border village of Baarle-Hertog, which famously has non-contiguous bit of the Netherlands in Belgium and vice versa.

(Editing by Philip Blenkinsop/)