The project begins with the main dam structure near the Saint Louis River bridge on MN-210. Water flows out of this structure and into the historic Saint Louis River channel. Water also backs up behind the dam forming Thomson Reservoir, which is about one square mile in size. A second dam structure and outlet allows water to flow into Forbay Canal. That 2 mile long canal feeds into a mile long set of underground pipes, which carry the water to the power plant. While the power plant is 3 miles from the dam, the river channel takes a bit over 5 miles to reach the power plant.
While most visitors see only the dam structure near the Saint Louis River channel, the dam is actually composed of many smaller dam segments. Some of these segments have been rebuilt and merged over the years. Here is a current listing from the National Dam Inventory:
| Dam ID | Structure | Width | Height | ||
|---|---|---|---|---|---|
| MN00604 | Thomson | 1600 | 15 | ||
| MN83020 | Thomson Dam No 1-1/2 | 90 | 10 | ||
| MN83021 | Thomson Dam No 2A, 2B | 530 | 23 | ||
| MN83022 | Thomson Dam No 2-1/2 | 130 | 9 | ||
| MN83023 | Thomson Dam No 3, 2-3/4, 3, 3A, 4, 4A | 1322 | 38 | ||
| MN83024 | Thomson Dam No 5 | 100 | 23 | ||
| MN83025 | Thomson Dam No 5-1/2 | 115 | 23 | ||
| MN83026 | Thomson Dam No 6 | 125 | 51 | ||
| MN83027 | Thomson Dam No 8 | 100 | 12 | ||
| MN83028 | Thomson Dam No 9 | 100 | 11 | ||
| MN83029 | Thomson Dam No 10 | 80 | 11 | ||
| MN83030 | Thomson Dam No 11, 11-1/2, Gate House | 365 | 17 | ||
| MN83031 | Thomson Dam No 12 | 450 | 12 |
The Thomson Water Project was built by Great Northern Power in 1907. Great Northern Power was an operating division of the Great Northern Railroad. It was later transferred to the Saint Louis Power Company. Today, it is known as the Thomson Energy Center, which is owned by Minnesota Power, which is a division of Allete, Inc.
