| Holmes Run | |
| Image Alt: | In the foreground is a rocky shallow stream that forks into two a short ways off from the photographer. There is an island in the right fork so that it joins the left fork in two places. Beyond the banks, a grove of deciduous trees rise into blue skies. |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Virginia |
| Mouth Location: | Cameron Run |
| Mouth Coordinates: | 38.8076°N -77.1112°W |
| Length: | 10.5miles |
| Custom Label: | GNIS feature ID |
| Custom Data: | 1478779[1] |
Holmes Run is a stream in the Cameron Run Watershed in Northern Virginia. It runs through Fairfax County and the City of Alexandria. It is a first-order tributary of the Potomac River.
Its headwater is near the junction of I-495 and I-66. It crosses the region in a southeasterly direction for ten and a half miles until it merges with Backlick Run to form Cameron Run. Cameron Run becomes Hunting Creek and empties into the Potomac River just south of the Woodrow Wilson Bridge.
In 1913–1915 the Alexandria Water Company built a dam on Holmes Run in order to create Lake Barcroft as a potable water reservoir for Alexandria. In the early post-war era, Alexandria began to exceed the capacity of Lake Barcroft and in 1949 discontinued its use in favor of Occoquan Reservoir.
As an urban river, Holmes Run has in places been heavily channelized, but also significant portions have been developed as urban greenspace as Holmes Run Trail.
Above Lake Barcroft its route makes up the border of West Falls Church and Annandale.