The area's geological history was heavily influenced by glaciation, and the several large glacial lakes have filled the river valley over the last 12,000 years.

The North Thompson passes by several small communities, the most notable being Blue River, Clearwater & Barriere.

The Clearwater, the North Thompson's largest tributary, drains much of Wells Gray Provincial Park.

From Ashcroft to Lytton, the river is completely confined within Thompson Canyon, making for spectacular scenery.

The Thompson River valley has existed in some form for at least 50 million years; however, for much of its history, it did not drain to the southwest into the Pacific Ocean as it does today.

[6] This flow direction is estimated to have ended approximately 2 million years ago, as the Pleistocene era of heavy glaciation began.

This flow direction was influenced by large ice buildups in the Thompson valley, which created extensive glacial lakes.

The ice moved out of the Thompson River region approximately 11,000 BCE, and migration by the ancestors of the Nlaka'pamux and Secwepemc people is thought to have occurred soon after.

[11] The South Thompson has the watershed's oldest dated evidence of human habitation, at the Gore site near Pritchard.

The human remains date to 8250 BCE, and bone analysis suggests the person was a hunter with small amounts of his protein coming from salmon.

[13] The first documented traverse of the Thompson from Kamloops to Lytton was by Hudson's Bay Company governor George Simpson in 1828.

[14] More Europeans entered the Thompson River valley in the early to mid 1800s, drawn by the fur trade and small gold rushes.

The river is home to large populations of Pacific salmon, including coho, sockeye, pink and chinook.

Coastal rainbow trout (Oncorhynchus mykiss irideus), including an anadromous variety called steelhead, are found in the river along with a local strain the Kamloops rainbow trout which occurs in Kamloops Lake at the Thompson River headwaters and other nearby lakes.

[16] Several bird species are found in Thompson River environments, including osprey, merganser, wood ducks, and American dippers.

From the 1950s through the early 1990s the Thompson River was considered one of the premier steelhead angling destinations in North America.

[20] By the late 1990s, steelhead populations began to decline due to a wide variety of adverse environmental conditions and overfishing by commercial and First Nations gill netters.