Two hundred and sixty species of Dytiscidae are known from Canada and Alaska, making this the largest family of aquatic beetles in the region. These beetles occur in a wide variety of shallow water habitats. The richest fauna is in the emergent vegetation zone along the edges of pools, small ponds and small, slow streams. A number of species are characteristic of cold water habitats such as small seepages and springs, and bog, forest, alpine and arctic pools. Clear, gravelly streams and saline ponds each contain distinctive groups of species. 

Adults are predators or scavengers on dead animals while all larvae are apparently predaceous. The range of prey taken probably is determined by what prey of suitable size is available, but some hydroporines feed largely on microcrustacea while some colymbetines prey mainly on culicid larvae. As far as is known or can be inferred, all species in the fauna are univoltine or semivoltine. Most species overwinter as adults but timing of breeding and occurrence of larval stages vary greatly among species. Representative larvae of most genera have been described, but larvae are known for only a small percentage of species. 

The family is relatively well known taxonomically. The principal taxonomic problems include: relating the northern Nearctic fauna with that of the Palaearctic; analysing and interpreting patterns of geographical variation which in many species are complex; development of supraspecific classification, especially within the larger genera. Identification of species may be very difficult as differences between species are often subtle thus there is a need for additional character analysis to provide better species definitions and characters for their recognition. Reviews and revisions of many genera have been, or are being, prepared but no single publication treats the entire fauna.

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