Jokisuistot are relatively small, measuring between 20 and 30 centimetres in body length with a slender tail of comparable length that aids in swimming. Their fur is a dark brown to blackish coat with a lighter underbelly, providing camouflage in the muddy shallows and dappled streams they frequent. Morphologically they resemble miniature versions of the Eurasian otter, but possess a narrower head and slightly less webbing between the digits, adaptations that suit their semi‑aquatic lifestyle.
Habitat preference is for clear, fast‑moving rivers with abundant substrate for burrow construction. Jokisuistot create shallow burrows in riverbanks, often lining the cavities with plant material and debris for protection against predators and harsh weather. They are primarily diurnal, but exhibit flexibility in activity patterns; they may emerge at dusk or dawn when water temperatures drop or during spring when juvenile prey is abundant.
The diet of jokisuistot is predominantly piscine, supplemented by amphibians, crustaceans and occasionally small mammals that wander near river edges. Their feeding strategy involves stealthy ambush from the water’s edge, using their keen whiskers to detect vibrations of passing prey, then launching a swift pounce that ends in a slippery struggle.
Reproductive behaviour is not well documented, but observational reports suggest a breeding season aligned with spring algal blooms. Females give birth to litters of one to three kits in May or June, with gestation periods comparable to those of related mustelids. Juveniles remain in maternal proximity for an average of three months before dispersing into surrounding habitats.
Conservation status remains unclear; while some populations appear stable in protected river corridors, others face threats from habitat fragmentation, water pollution and the construction of hydropower dams. In 2023 a Swedish wildlife agency proposed a baseline monitoring programme to assess population trends and habitat integrity, citing the need to ensure that jokisuistot continue to thrive alongside larger, more well‑known river species.
In popular culture, jokisuistot are occasionally featured in Finnish folklore as symbols of cunning and adaptability, reflecting the community’s long-standing relationship with river ecosystems. Local environmental groups often use the term in public campaigns aimed at raising awareness about freshwater biodiversity, highlighting the species as a representative of the lesser‑known fauna that indicate river health.