At first, the Heidezee was a shallow but extended body of water, with high tides but also a predominance of fresh water.
The deposits of the rivers caused the land to become only submerged at high tides.
From that moment on the area was called the Bergse Veld ("Fields of Geertruidenberg") and, later on (during the 18th century), the Biesbosch (although a small patch of swamp had been known as Biesbosch even before the flood).
A network of interconnecting creeks, mudflats and forested areas arose, which served as a sort of inland delta of the large rivers feeding it.
A significant result of this was that the former estuary arms of the Rhine and Meuse, further north-west, were devoid of much of the inflow of fresh water.
This caused the rivers to fill with deposits, so the important shipping route between Rotterdam and the inland areas was no longer usable.

During the last centuries, conditions changed significantly.
Most of the Biesbosch was reclaimed and turned into polders.
The Rhine-Meuse connection with Rotterdam was restored by preventing the build-up of deposits by artificial means.
Most of the Biesbosch creeks were closed off at their upstream end to lower the risk of flooding.
The confluence of the Meuse and Rhine rivers was closed off as well and the Meuse received a new, artificial mouth: the Bergse Maas.
By separating rivers Meuse and Rhine before they reach the Biesbosch, their flow can be controlled better.
A second ship canal was created to better distribute the flow of the river Rhine as well: the Nieuwe Merwede, which divides the Biesbosch into two parts: the "lesser" Biesbosch, now the southeastern part of the Island of Dordrecht, and the "greater" Biesbosch.
As a result of these hydrological changes, the Biesbosch lost its function as a river delta and now only receives water directly from the rivers in times of high discharges.

During World War II, the area was used by Dutch residents to hide out from the German occupation forces in the Netherlands.
A resistance group was formed that, late in the war, captured Germans fleeing to the north from what was then the Allied-held south of the Netherlands.
In the winter of 1944, the area was crossed by refugees from the occupied north, while, at the same time, it was being used to smuggle medicines to the north.
The people that coordinated these activities are known as the Biesbosch crossers and are commonly regarded as national heroes.
Many Dutch books and a few movies are based on this resistance group.

Before 1970 a connection with the sea existed, and the tidal differences were, on average, two meters.
Despite the diminished inflow of the Meuse and Waal rivers, fresh water continued to dominate.
The tidal differences almost disappeared after 1970 when the Delta Works closed the Haringvliet and with it the Biesbosch's direct connection with the sea.
Only in the northern part of the Biesbosch (the so-called Sliedrechtse Biesbosch) some of the tidal difference remained (20–80 cm on average).
The diminishing of the tidal difference caused a dramatic transformation of the Biesbosch, which mostly changed into a willow forest with small remnants of the once mighty delta streams.
The creation of the Haringvlietdam also blocked the main route for migrating fish.
The influence of both rivers and sea had now mostly gone.
At first, the Heidezee was a shallow but extended body of water, with high tides but also a predominance of fresh water. The deposits of the rivers caused the land to become only submerged at high tides. From that moment on the area was called the Bergse Veld ("Fields of Geertruidenberg") and, later on (during the 18th century), the Biesbosch (although a small patch of swamp had been known as Biesbosch even before the flood). A network of interconnecting creeks, mudflats and forested areas arose, which served as a sort of inland delta of the large rivers feeding it. A significant result of this was that the former estuary arms of the Rhine and Meuse, further north-west, were devoid of much of the inflow of fresh water. This caused the rivers to fill with deposits, so the important shipping route between Rotterdam and the inland areas was no longer usable.
During the last centuries, conditions changed significantly. Most of the Biesbosch was reclaimed and turned into polders. The Rhine-Meuse connection with Rotterdam was restored by preventing the build-up of deposits by artificial means. Most of the Biesbosch creeks were closed off at their upstream end to lower the risk of flooding. The confluence of the Meuse and Rhine rivers was closed off as well and the Meuse received a new, artificial mouth: the Bergse Maas. By separating rivers Meuse and Rhine before they reach the Biesbosch, their flow can be controlled better. A second ship canal was created to better distribute the flow of the river Rhine as well: the Nieuwe Merwede, which divides the Biesbosch into two parts: the "lesser" Biesbosch, now the southeastern part of the Island of Dordrecht, and the "greater" Biesbosch. As a result of these hydrological changes, the Biesbosch lost its function as a river delta and now only receives water directly from the rivers in times of high discharges.
During World War II, the area was used by Dutch residents to hide out from the German occupation forces in the Netherlands. A resistance group was formed that, late in the war, captured Germans fleeing to the north from what was then the Allied-held south of the Netherlands. In the winter of 1944, the area was crossed by refugees from the occupied north, while, at the same time, it was being used to smuggle medicines to the north. The people that coordinated these activities are known as the Biesbosch crossers and are commonly regarded as national heroes. Many Dutch books and a few movies are based on this resistance group.
Before 1970 a connection with the sea existed, and the tidal differences were, on average, two meters. Despite the diminished inflow of the Meuse and Waal rivers, fresh water continued to dominate. The tidal differences almost disappeared after 1970 when the Delta Works closed the Haringvliet and with it the Biesbosch's direct connection with the sea. Only in the northern part of the Biesbosch (the so-called Sliedrechtse Biesbosch) some of the tidal difference remained (20–80 cm on average). The diminishing of the tidal difference caused a dramatic transformation of the Biesbosch, which mostly changed into a willow forest with small remnants of the once mighty delta streams. The creation of the Haringvlietdam also blocked the main route for migrating fish. The influence of both rivers and sea had now mostly gone.
Biesbosch National Park