The Chain Islets and Great Chain Island are located in Oak Bay, in the Juan de Fuca Strait, less than 2 km from the suburbs of Victoria, British Columbia. The site includes a cluster of at least 18 small islets and rocks in Mayor Channel. The low round islets are rocky and barren except for Great Chain Island that supports a nearly continuous grass and herbaceous cover and occasional shrub thickets. Shoreline features include a few steep faces, rocky outcroppings, boulders, crevices and small gravel beaches. The islets are surrounded by shallow water from which many rocky reefs emerge. The site includes the marine waters within a radius of approximately 700 m. Harbour Seals are regular in summer and the natural Gulf of Georgia meadow habitat, which has been eliminated by disturbance from most sites in British Columbia, supports rare flora such as Golden Indian Paintbrush, California Buttercup and Snakeroot Sanicle.

Chain Islets and Great Chain Island is a site of global importance, supporting a significant breeding population of Glaucous-winged Gulls, and a migratory population of Brandts Cormorants. Surveys in 1986 and 1987 recorded 2,432 pairs of Glaucous-winged Gulls (over 1% of the North American population) breeding on the islands. The colony of Glaucous-winged Gulls is the largest in British Columbia and, together with two other similar sized colonies in the strait (Mandarte and Mitlenatch), supports a quarter of the breeding Glaucous-winged Gulls in British Columbia. In fall, up to 2,000 Brandts Cormorants have been recorded in the area, which is over 2% of the estimated world population. A Pelagic Cormorant colony is also present at this site. In 1987, the population peaked at 248 pairs, but since that time has steadily declined to only 7 pairs in 1999.

Additionally, 510 pairs of Double-crested Cormorants, which in British Columbia nest only in the Strait of Georgia, were recorded nesting in these islets. This is the second largest colony of this species in the province. Pigeon Guillemots and American Black Oystercatchers also nest on the islets, and Harlequin Ducks occur seasonally among the reefs and islands.

The site is part of the British Columbia Provincial Ecological Reserve # 94, Oak Bay Island. Despite this designation, the proximity to Victoria has led to some disturbance from boaters who land to picnic and party on the islands. The breeding seabirds are susceptible to disturbance and the local plant communities are sensitive to damage from trampling.