Cowichan Bay is a community situated on the south shore of an estuary shared by the Cowichan and Koksilah Rivers that form 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 is derived from the Quamichan First Nation of the Coast Salish people. The Last Glacial Maximum began about 33,000 years ago during the Late Pleistocene, and the growth of continental ice sheets reached a maximum between 26,500 and 20,000 years ago causing drought, desertification, and a large drop in sea level. During this glacial period, the ice was thousands of feet thick (hundreds of meters), and so heavy that Vancouver Island was depressed by more than 500 feet (150 m). Around 15,000 years ago the climate began to warm, and the ice sheets slowly melted and retreated causing the land to rebound. Moving and melting ice cut major features into the landscape including the U-shaped Cowichan Valley, the deep depression of Lake Cowichan, and the discharging meltwater formed the braided channels of the Cowichan River. The retreating ice sheet deposited large volumes of glacial till consisting of a mixture of soil, clay, sand, and gravel. Ancient rivers transported these sediments to the lowlands fringing the coast and into the Cowichan Bay estuary forming the 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, draining a watershed of 303,198 acres (122,700 ha) which includes the many small streams draining into Lake Cowichan from the headwaters. The Koksilah River begins from the south flank of Waterloo Mountain and drains a watershed of 74,132 acres (30,000 ha) south of the Cowichan River valley and flows 27 miles (44 km) to Cowichan Bay. There are no large lakes in the Koksilah watershed which is a rain-dominated hydrological regime with additional contributions from groundwater aquifers.

Humans first arrived in the Cowichan Region about 10,000 to 8,000 years ago and adapted to the seasonal climate patterns by establishing permanent villages as well as seasonal fish camps according to the natural cycles of spawning salmon and migratory birds and mammals. The area provided an abundant food supply, medicinal plants, and construction materials such as western red cedar for houses and canoes. The Quamichan oral tradition has a creation story about the first person named Syalutsa who thousands of years ago fell from the sky and landed on a ridge near the Koksilah River, and not long after, was followed by his brother named Stuts’un. The origins of the name Koksilah, which means ‘place having rush-mat shelters’, date to a time when two women from Sooke traveled to find Syalutsa and made a rush-mat shelter on the ridge. 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 commonly called the Douglas Treaties with 14 First Nations. The treaties extinguished First Nations territories and allowed European settlers to take possession of 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 and introduced private land ownership by selling land in the area to settlers. By the 1860s, logging and land clearing were well underway, and the low-lying areas of the region were being settled by farmers. The Cowichan River was severely modified to allow log rafting and log drives to the estuary. The original settlement was near the mouth of the Cowichan River where the Quamichan had a village. One of the biggest obstacles to that location was the shallow water at the head of the bay. Goods brought to the trading post had to be barged from boats anchored in deeper water. This was time-consuming and extremely difficult, so eventually, the south shore of the bay with access to deeper water made for a better settlement site. The village of Cowichan Bay thrived and steamer service from Victoria was the major link for goods and people before a railway was built. By the late 1800s, about 148,263 acres (60,000 ha) were occupied by settlers including prime oceanfront and riverfront lands along the Cowichan and Koksilah Rivers. In 1884, the Esquimalt and Nanaimo (E&N) Railway Company was formally established, with James Dunsmuir as president and holding almost half of the company’s shares. Over the following years, the E&N hauled about 400,000 cars of timber out of the river valleys. In 1905, the Canadian Pacific Railway bought the E&N and extended the railway through the tidal flats of the Cowichan estuary connecting the seaport with inland logging operations. By 1920, 18 logging companies employed 1,200 men in logging the Cowichan valley forests. Through the 20th century, the economy of Cowichan Bay was largely based on fishing, agriculture, and timber exports. When that economic base started declining, it was replaced with tourism and recreational water activities.

In 1957, a paper mill owned by British Columbia Forest Products in Crofton, a coastal community about 8 miles (13 km) north of Cowichan Bay, needed to access a more dependable year-round water supply and built a weir at the outlet of Lake Cowichan to raise the lake water level and provide more water storage. During the fall and winter or periods of high precipitation, gates are left open, and the weir does not control river flow or lake levels. When inflow to the lake begins to drop in the spring, the gates are operated to maintain lake level near the crest of the weir. Operation of the weir usually starts in April and continues until September or October when abundant precipitation resumes, and the lake is replenished. During this control period, the weir is operated to store water in the lake and maintain a flow rate in the Cowichan River of at least 247 cubic feet (7 cubic meters) per second. This flow rate is required to maintain water quality, habitat for spawning salmon and other fish, the economic needs of the Crofton mill, agricultural requirements, and the drinking water supply for the community of Lake Cowichan plus four other communities in the Cowichan Valley Regional District. This area has changed greatly over the years as a result of human activities in the marine environment, development of the surrounding shores and intertidal flats, and in the watershed. In response to these changes, the Cowichan Estuary Environmental Management Plan was developed and completed in 1987 to provide a framework for future management of the estuary. The management plan encompasses multiple jurisdictions and land uses including the village of Cowichan Bay, First Nations traditional lands, industrial leases of Crown lands, parcels under the management of the municipality of North Cowichan, the Cowichan Valley Regional District, national and international conservation organizations, and private landholders. Since the 1990s, the effects of climate change on the volume and timing of precipitation have caused challenges for weir management in which the lake level, discharge rate in the river, salmon priorities, and rainfall predictions are all complicating factors. In 2019, the lake fell below the critical storage level and electric pumps were required to transfer water out of the lake and into the river to keep the Cowichan River flowing. Most recently, efforts to improve the health of the Cowichan and Koksilah Rivers estuary is due to a coalition of non-profits, government and non-government organizations, and individuals who are actively involved with estuarine habitat enhancement projects and who lobbying for better stewardship of the estuary against strong opposition from commercial and industrial interests. The non-profits include the Cowichan Estuary Preservation Society, Ducks Unlimited, Nature Trust, and Cowichan Land Trust. Read more here and here. Explore more of Cowichan Bay here: