The Thompson River is the largest tributary of the Fraser River, in the Cariboo Mountains west of the community of Valemount and flows generally south towards Kamloops and the confluence with the South Thompson. For most of its length, the river is paralleled by Highway 5 and the Canadian National Railway (both of which cross the river a couple times). The North Thompson passes by several small communities, the most notable being Blue River, Clearwater and Barriere.
The North Thompson picks up the Clearwater River at the town of Clearwater. The Clearwater, the North Thompson's largest tributary, drains much of Wells Gray Provincial Park.
A notable feature along the North Thompson is Little Hells Gate, a mini-replica of the much larger rapid on the Fraser downstream from the mouth of the Thompson. About upstream from the small town of Avola, the river is forced through a narrow chute only about wide creating a rapid that resembles the Fraser's famous rapid.
Mainstream
thumb|upright=1.4|The darker waters of the Thompson meet the Fraser at Lytton.
At Kamloops, the combined Thompson River flows from the confluence of the North and South Thompson Rivers before reaching Kamloops Lake, which is roughly in length, ending at the town of Savona. From there it flows in a meandering course westwards through a broad valley area. At Ashcroft, the Thompson Canyon begins and the river turns southwestward to its confluence with the Fraser. The river is paralleled by the Trans-Canada Highway, the Canadian Pacific Railway and the Canadian National Railway.
From Ashcroft to Lytton, the river is completely confined within Thompson Canyon, making for spectacular scenery. The Thompson River joins the Fraser River in Lytton. There is a striking stretch of dark black cliffside just downstream from Ashcroft and visible from the Logan Lake-Ashcroft highway is officially named the Black Canyon. Just below the town of Spences Bridge was the site of a major rail disaster in the early 20th century<!--found pics, no details of crash/washout-->. Communities along this section are Bighorn, Shaw Springs, and Goldpan.
Geology
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. Geologists believe water from the river flowed northward, through the Cariboo region, eventually entering what is the modern-day Peace River drainage basin and ending up in the Arctic Ocean. This flow direction is estimated to have ended approximately 2 million years ago, as the Pleistocene era of heavy glaciation began.
Glacial lakes
During the era of massive glaciers in the Thompson River valley, water from the area likely drained eastward, through the Shuswap Lake area into what is now the Columbia River drainage. This flow direction was influenced by large ice buildups in the Thompson valley, which created extensive glacial lakes. Two large glacial lakes, Glacial Lake Thompson and Glacial Lake Deadman, occupied much of the modern river's course from 13,000 BCE to 10,000 BCE. These deep, narrow, ribbon-shaped lakes held large volumes of water; Glacial Lake Thompson held nearly at its highest point. The lake stretched from Spences Bridge in the west to the eastern reaches of Shuswap Lake, as well as far up the northern reaches of the North Thompson river valley. The last large glacial lake, Lake Deadman, was drained by a catastrophic ice dam failure, called a , in about 10,000 BCE. This event released as much as of water southwest into the Fraser River system, possibly depositing sediments as far away as the Salish Sea, more than away. From this point, the Thompson waters stopped flowing eastward into the Columbia River system, and the river became a tributary of the Fraser. The area downstream from the town of Ashcroft is prone to landslide events; eight major events between 1880 and 1982 have been recorded. Several of them have obstructed the river, and caused large, temporary lakes. An 1880 slide caused the formation of a short-lived lake over 14 kilometres long with a maximum depth of 18 metres. These slides have caused major damage to the rail lines and farming operations in the river valley. Heavy irrigation has been blamed for some of the events.
Conservation of the Thompson's fisheries, especially its salmon population, has been a focus of provincial, federal, and international bodies, such as the Department of Fisheries and Oceans (DFO) and the Pacific Salmon Commission.
thumb|Hwy 5 bridge, first crossing of N. Thompson River after emerging from the Cariboo Mountains
Angling
From the 1950s through the early 1990s the Thompson River was considered one of the premier steelhead angling destinations in North America. The river hosted large runs of both summer and winter run anadromous coastal rainbow trout (Oncorhynchus mykiss irideus). In the late 1980s the runs were estimated at over 10,000 fish. The river attracted anglers from around the world seeking powerful Thompson River steelhead. In 1982, the average male winter run Thompson River steelhead was . 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. In 2016, annual steelhead numbers entering the Thompson were estimated to be less than 400 fish. Low numbers have prompted conservation organizations and sportsman's associations to petition Committee on the Status of Endangered Wildlife in Canada (COSEWIC), for Canada's Species At Risk Act (SARA) protections. The river is subject to catch and release angling only for steelhead and has severely restricted seasons to protect the wild stocks of remaining steelhead.
Whitewater rafting
The rapids of the lower Thompson are used for recreational whitewater rafting. The first commercial rafting operation on the river began in the 1970s, based out of Spences Bridge. Notable whitewater features on the lower river include the Frog, named for a frog-shaped rock formation, and the Jaws of Death, named by CPR engineers. Rapids on the river reach up to Class 5 on the International Scale of River Difficulty.
Major Tributaries
thumb|The South Thompson River valley, near [[Monte Creek]]
North Thompson River
- Albreda River
- Thunder River
- Mud Creek
- Blue River
- Mad River
- Raft River
- Clearwater River
- Barrière River
South Thompson River
- Little River (via Little Shuswap Lake from Shuswap Lake)
- Chase Creek
- Monte Creek
Mainstream
- Tranquille River (via Kamloops Lake)
- Deadman River
- Bonaparte River
- Oregon Jack Creek
- Nicola River
- Murray Creek
- Skoonka Creek
- Nicoamen River
- Botanie Creek
See also
- List of tributaries of the Fraser River
- List of rivers of British Columbia
- List of crossings of the Thompson River