[4] Bull trout may be either migratory, moving throughout large river systems, lakes, and the ocean, or they may be resident, remaining in the same stream their entire lives.

[2][9] Bull trout have exacting habitat demands, requiring water temperatures generally below 55 °F (13 °C), clean gravel beds, deep pools, complex cover such as snags and cut banks, and large systems of interconnected waterways to accommodate spawning migrations.

[11] During the early life stages, bull trout are often found in small, low-gradient streams or near the shores of larger rivers and lakes.

Bull trout rely on clean, cold water and gravels of specific sizes for successful reproduction.

[16] These movements often occur during the non-spawning season when the fish search for suitable feeding grounds or escape unfavorable conditions such as high water temperatures or low oxygen levels.

[16] In some cases, bull trout have been observed moving between different river basins, crossing over mountain ranges, and even traversing large lakes.

[17] These long-distance dispersal events contribute to gene flow between isolated populations, maintaining genetic diversity and increasing the species’ resilience.

[14] By tracking the movements of individual fish and analyzing their genetic makeup, researchers can gain valuable insights into dispersal patterns, population dynamics, and potential barriers to migration.

In coastal Washington, some of the southernmost populations of bull trout feed heavily on salmon eggs and fry, as well as fish.

[26] Bull trout reproduction requires cold water and very low amounts of silt, both of which are negatively impacted by road building and logging.

[29]: 71–72  By the recommendation of COSEWIC,[29]: iv  the Saskatchewan-Nelson Rivers population in Alberta was listed as threatened under the Species at Risk Act in 2019.

[citation needed] The first recorded use of the name "Dolly Varden" for a fish species was applied to members of S. confluentus caught in the McCloud River in northern California in the early 1870s.

David Starr Jordan, while at Stanford University, included an account of this naming of the Dolly Varden trout in one of his books.

In 1874, Livingston Stone, a naturalist working for the U.S. government, wrote of this fish:[30] Also called at (Upper) Soda Springs the 'Varden' trout.

[citation needed] Ironically, the original "Dolly Varden" trout (i.e., S. confluentus) apparently likely became extirpated in the McCloud River in the 1970s, although reports continue of its being caught.

Other fish species, typically introduced trout, outcompete S. confluentus, and can interbreed with them, resulting in sterile hybrids.

[31] The "Dolly Varden" name is also applied to the other subspecies of S. malma, the S. m. krascheninnikova, and S. m. miyabei, found in Lake Shikaribetsu on the island of Hokkaidō in Japan.