The Winooski River begins in the town of Cabot and flows 90 miles to Lake Champlain in Colchester. The watershed drains approximately 1,080 square miles in central Vermont, encompassing all of Washington County, about half of Chittenden County, and portions of Lamoille and Orange Counties. The Winooski River is the largest tributary watershed to Lake Champlain. It includes almost 10% of the land area of Vermont.
Based on 1997 National Resource Inventory data, approximately 72% of the watershed is forested, 12% is in agriculture and 9% is considered developed land which includes rural roads and urban and built up land. Water accounts for 5% of the total acreage and the remaining percentage is in miscellaneous land uses such as gravel pits, farmsteads, marshland and isolated single rural residences. Approximately 75,600 acres or 11 % of the 690,000-acre watershed are owned by the State of Vermont and managed by the Agency of Natural Resources. The Federal government owns 12,900 acres of land in the watershed. Since 1982, the percentage of land in agriculture has gone from 16% to 12% and the percentage of urban land has increased from 6% to 9%. The makeup of urban/developed land, not including roads or utilities, in the watershed that is dedicated to residential use ranges between 70 and 80 percent. Commercial/industrial use ranges between 15 and 20 percent.
The river and tributaries from the head to Montpelier are mostly narrow and steep with heavily timbered valleys. Below Montpelier, the river has a relatively consistent gradient with fertile open land well suited for cultivation except for a few steep gorges. The Middlesex, Bolton and Winooski gorges facilitate the harnessing of hydropower and have attracted mills and the development of towns dating to the late 1700s.
The river has seven major tributaries: Little River, North Branch and Kingsbury Branch enter from the north and the Huntington River, Mad River, Dog River and Stevens Branch enter from the south.
Kingsbury Branch begins in Woodbury, flows through Calais, and enters the Winooski River in East Montpelier. It is 12 miles long and has a watershed area of 34,500 acres.
Stevens Branch: begins in Williamstown, flows through Barre, and enters the Winooski River in Berlin. It is 13 miles long and has a watershed area of 82,800 acres. The Jail Branch begins in the town of Washington, flows through the town of Orange and enters the Stevens Branch in Barre. It is 16 miles long and passes through a retention dam built after the 1927 flood. The watershed area is 31,050 acres.
North Branch begins in Elmore and flows through Worcester, Middlesex, and East Montpelier and enters the Winooski River in Montpelier. It is 18 miles long and passes through a retention dam built after the 1927 flood. It has a watershed area of 48,300 acres.
Dog River: begins in Roxbury, flows through Northfield, and enters the Winooski River in Berlin. It is 18 miles long and has a watershed area of 60,030 acres.
Mad River: begins in Granville, flows through Warren and Waitsfield and enters the Winooski River in Moretown. It is 26 miles long and has a watershed area of 91,080 acres.
Little River begins in Morristown, flows through Stowe and enters the Winooski River in Waterbury. 15 miles long and passes through a retention dam built after the 1927 flood. It has a watershed area of 71,070 acres.
Huntington River: begins in Fayston, flows through Buel’s Gore, Starksboro, Huntington, and enters the Winooski River in Richmond. It is 20 miles long and has a watershed area of 43, 470 acres.
The Lower Tributaries include: Mill Brook flows through Jericho. It is 9.5 miles long and has a watershed area of 10,350 acres. Muddy Brook outlets from Shelburne Pond, flowing through Shelburne, South Burlington and Williston to the Winooski River. It is 5.5 miles and has a watershed area of 16, 560 acres. Allen Brook flows through Williston. It is 10 miles long and has a watershed area of 6,900 acres. Alder Brook flows through the town of Essex. It is 10 miles long and has a watershed area of 6,762 acres.