Small populations are scattered throughout the Mississippi-Great Lakes basin extending to Colorado, New Mexico, Kentucky, Tennessee, etc., though some of these areas are not native to the species.

Harvesting of trees around riparian environments is having a large effect of the stream ecosystem where the brook stickleback resides.

[7] The brook stickleback was first formally described as Gasterosteus inconstans in 1840 by the American naturalist Jared Potter Kirtland with its type locality given as Trumbull County, Ohio.

Most of the year the colouring is grayish or olive green with a varying amount of indistinct mottling, but during the spawning season, males are nearly black and females have darker and lighter patches.

[11] Culaea inconstans occurs throughout the southern half of Canada and the northern part of the eastern United States.

Populations also exist in Colorado and Nebraska to the west, and in Alberta, Saskatchewan, Manitoba, and the Northwest Territories to the north.

Though these are typically the native ranges of the brook stickleback, the species has been introduced to Alabama, Kentucky, Tennessee, northwestern Colorado, Wyoming, northeastern Utah and California, and even in parts of South Dakota and Washington State.

Nebraska does have brook stickleback populations, but they are generally found in small streams in the northern portion of the state.

This can lead to a destruction of habitat, increase in silted waterways, alteration of stream nutrient transport, and damaged breeding grounds.

[2] As with a large geographical distribution, this species also lives in a wide range of flowing water habitats.

Though the species can thrive in these habitats, primary spawning, breeding, and rearing grounds are located in shallow (< 1.5m) near shore environments with high vegetation cover and low velocity water.

With its small size, this species of stickleback has evolved piercing spines and protective plates to hinder predators.

In a lab study, adult water bugs (Lethocerus americanus) and dragonfly nymphs (Aeschna spp.)

Examples of these fish predators include yellow perch (Perca flavescens), rock bass (Ambloplites rupestris), creek chub (Semotilus atromaculatus), burbot (Lota lota), central mudminnow (Umbra limi), smallmouth bass (Micropterus dolomieu), largemouth bass (Micropterus salmoides), northern pike (Esox lucius), brook trout (Salvelinus fontinalis), rainbow trout (Oncorhynchus mykiss) and round goby (Neogobius melanostomus).

Brook sticklebacks migrate annually up affluent streams and creeks of rivers and lakes during the spring to spawn in weedy areas.

During this process, studies have shown that the female makes acoustic noises, which is thought to advertise to sneaker males, as this can increase the proportion of eggs fertilized.

[6] Although the Nature Conservancy has listed the brook stickleback as level S3 (vulnerable), the numbers of this species aren't threatened.

[17] The brook stickleback can be found from the northern parts of the Canadian interior all the way down to southern reaches of the United States.