The Mackenzie River's watershed is considered one of the largest and most intact ecosystems in North America, especially the northern half.
Approximately 63% of the drainage basin, or 1,137,000 km² (439,000 sq mi), is forested (mostly boreal forest).
Wetlands comprise about 18%, or about 324,900 km² (125,400 sq mi), of the basin.
More than 93% of forested areas are virgin old-growth forest.
However, human activities such as oil extraction have threatened water quality in the headwaters of the Mackenzie River.
In addition, a warming climate in northern parts of the watershed is melting permafrost and destabilizing soil through erosion.

Most of the taiga consists of black spruce, aspen and poplar forest.
In the north, the river's shores are lined with sparse vegetation like dwarf birch and willows, as well as extensive areas of muskeg and peat bogs.
South of Great Slave Lake, there are much larger reaches of temperate and alpine forest, prairie, and fertile floodplain and riparian habitat.

There are 53 fish species in the basin, none of them endemic.
The Mackenzie River has a similar range of fish fauna to the Mississippi River system.
It is believed that the two river systems were connected during the Ice Ages by meltwater lakes and channels, allowing fish in the two rivers to interbreed.
Fish in the Mackenzie River proper include the northern pike, several minnow species, and lake whitefish.
Fish in the southern half of the watershed are genetically isolated from those of the northern half due to large rapids on the Slave River preventing fish from swimming upstream.

Migratory birds use the three major deltas in the Mackenzie River basin – the Mackenzie Delta and the inland Slave and Peace-Athabasca Deltas – as resting and breeding areas.
The latter is located at the convergence of four major North American migratory routes, or flyways.
As recently as the mid-twentieth century, more than 400,000 birds passed through during the spring and up to a million in autumn.
Some 215 bird species in total have been catalogued in the delta, including species such as the whooping crane, peregrine falcon and bald eagle.
The construction of the W.A.C. Bennett Dam on the Peace River has reduced the seasonal variations of water levels in the delta, causing damage to its ecosystem.
Bird populations have seen a steady decline since the 1960s.

Water mammals such as beavers and muskrats are extremely common in the Mackenzie Delta and surrounding areas of muskeg.
The Mackenzie estuary is also a calving area for beluga whales.
The Mackenzie River's watershed is considered one of the largest and most intact ecosystems in North America, especially the northern half. Approximately 63% of the drainage basin, or 1,137,000 km² (439,000 sq mi), is forested (mostly boreal forest). Wetlands comprise about 18%, or about 324,900 km² (125,400 sq mi), of the basin. More than 93% of forested areas are virgin old-growth forest. However, human activities such as oil extraction have threatened water quality in the headwaters of the Mackenzie River. In addition, a warming climate in northern parts of the watershed is melting permafrost and destabilizing soil through erosion.
Most of the taiga consists of black spruce, aspen and poplar forest. In the north, the river's shores are lined with sparse vegetation like dwarf birch and willows, as well as extensive areas of muskeg and peat bogs. South of Great Slave Lake, there are much larger reaches of temperate and alpine forest, prairie, and fertile floodplain and riparian habitat.
There are 53 fish species in the basin, none of them endemic. The Mackenzie River has a similar range of fish fauna to the Mississippi River system. It is believed that the two river systems were connected during the Ice Ages by meltwater lakes and channels, allowing fish in the two rivers to interbreed. Fish in the Mackenzie River proper include the northern pike, several minnow species, and lake whitefish. Fish in the southern half of the watershed are genetically isolated from those of the northern half due to large rapids on the Slave River preventing fish from swimming upstream.
Migratory birds use the three major deltas in the Mackenzie River basin – the Mackenzie Delta and the inland Slave and Peace-Athabasca Deltas – as resting and breeding areas. The latter is located at the convergence of four major North American migratory routes, or flyways. As recently as the mid-twentieth century, more than 400,000 birds passed through during the spring and up to a million in autumn. Some 215 bird species in total have been catalogued in the delta, including species such as the whooping crane, peregrine falcon and bald eagle. The construction of the W.A.C. Bennett Dam on the Peace River has reduced the seasonal variations of water levels in the delta, causing damage to its ecosystem. Bird populations have seen a steady decline since the 1960s.
Water mammals such as beavers and muskrats are extremely common in the Mackenzie Delta and surrounding areas of muskeg. The Mackenzie estuary is also a calving area for beluga whales.
Mackenzie River