Cowichan Bay is a community located on the south shore of an estuary formed by the Cowichan and Koksilah rivers, which create an extensive tidal flat on the east coast of southern Vancouver Island, about 26 miles (42 km) north-northwest of Victoria and 4 miles (6 km) southeast of Duncan, British Columbia. The name Cowichan derives from the Quamichan First Nation of the Coast Salish people. The Last Glacial Maximum began around 33,000 years ago during the Late Pleistocene, when continental ice sheets reached their peak between 26,500 and 20,000 years ago, triggering drought, desertification, and a significant drop in sea level. During this period, ice up to thousands of feet thick (hundreds of meters) was so heavy that it depressed Vancouver Island by more than 500 feet (150 m). Around 15,000 years ago, the climate began to warm; the ice sheets slowly melted and retreated, allowing the land to rebound. Moving, melting ice sculpted the landscape, carving features such as the U-shaped Cowichan Valley and the deep depression of Lake Cowichan, while discharging meltwater formed the braided channels of the Cowichan River. The retreating ice sheet deposited vast amounts of glacial till—a mixture of soil, clay, sand, and gravel. Ancient rivers transported these sediments to the lowlands along the coast and into the Cowichan Bay estuary, forming extensive tidal flats. Today, the Cowichan River originates at the outlet of Lake Cowichan, at an elevation of 540 feet (164 m), and flows generally east-southeast for 31 miles (50 km) to the head of Cowichan Bay. It drains a watershed of 303,198 acres (122,700 ha) that includes many small streams feeding Lake Cowichan. The Koksilah River originates on the south flank of Waterloo Mountain, drains a 74,132-acre (30,000 ha) watershed south of the Cowichan River valley, and flows 27 miles (44 km) to Cowichan Bay. The Koksilah watershed contains no large lakes; its hydrology is dominated by rainfall, with additional contributions from groundwater aquifers.

Humans arrived in the Cowichan region between 10,000 and 8,000 years ago and adapted to seasonal climates by establishing permanent villages and fish camps aligned with salmon spawning and wildlife migrations. The area offered abundant food, medicinal plants, and construction materials such as western red cedar. According to Quamichan oral tradition, the first person, Syalutsa, fell from the sky and landed on a ridge near the Koksilah River. Soon after, his brother Stuts’un appeared. The name Koksilah—meaning “place having rush‐mat shelters”—derives from two women from Sooke who built a shelter on that ridge in search of Syalutsa. In the mid-1800s, Europeans reported seven cedar longhouses in the village of Koksilah at the head of Cowichan Bay. Between 1850 and 1854, Governor James Douglas negotiated land-sale agreements known as the Douglas Treaties with 14 First Nations, extinguishing indigenous territories and opening lands for farming, mining, and timber extraction. In 1858, the Hudson’s Bay Company established a trading post on the tidal flat at the mouth of the Cowichan River, introducing private land ownership. By the 1860s, logging and land clearing were under way. The Cowichan River was modified for log rafting, while the original settlement near its mouth struggled with shallow water. A site on the bay’s south shore, with better access to deeper water, was chosen. Steamer service from Victoria connected the thriving village until the railway arrived. By the late 1800s, settlers occupied about 148,263 acres (60,000 ha) along the Cowichan and Koksilah Rivers. The Esquimalt and Nanaimo Railway Company, established in 1884 under James Dunsmuir, hauled roughly 400,000 timber cars until the Canadian Pacific Railway extended the line in 1905. By 1920, 18 logging companies employed 1,200 men in the valley. Throughout the 20th century, Cowichan Bay’s economy relied on fishing, agriculture, and timber exports. As these industries declined, tourism and recreational water activities emerged as its new foundation, reflecting the region’s enduring adaptability.

In 1957, a paper mill in Crofton—a coastal community 8 miles north of Cowichan Bay and owned by British Columbia Forest Products—needed a dependable year-round water supply. It built a weir at Lake Cowichan’s outlet to raise the lake’s level and increase storage. In fall, winter, and high-precipitation periods, the gates remain open, leaving flow and levels unregulated. In spring, as inflow declines, the gates close to maintain the lake level near the weir’s crest, typically from April until September or October when renewed rain replenishes the lake. During this period, the weir stores water and guarantees a minimum flow of 247 cubic feet (7 cubic meters) per second in the Cowichan River. This flow is essential for water quality, salmon spawning, sustaining the Crofton mill, agriculture, and supplying drinking water to Lake Cowichan and four other communities in the Cowichan Valley Regional District. Marine development, alterations to shores and intertidal flats, and watershed modifications have transformed the area. In 1987, the Cowichan Estuary Environmental Management Plan was completed to guide future stewardship. The plan spans diverse jurisdictions and land uses: Cowichan Bay village, First Nations lands, Crown land industrial leases, North Cowichan municipal parcels, the Cowichan Valley Regional District, conservation organizations, and private owners. Since the 1990s, climate change has complicated weir management by altering precipitation, lake levels, river discharge, and salmon priorities. In 2019, when the lake dropped below its critical storage level, electric pumps were required to sustain river flow. Recent efforts to improve the health of the Cowichan and Koksilah Rivers estuary come from a coalition of nonprofits, government agencies, and individuals who undertake habitat-enhancement projects and lobby for better stewardship against commercial and industrial opposition. Nonprofits include the Cowichan Estuary Preservation Society, Ducks Unlimited, Nature Trust, and Cowichan Land Trust. Read more here and here. Explore more of Cowichan Bay and Vancouver Island here: