Definition: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Input: Passage: There are more than 20 major dams on the Willamette's tributaries, as well as a complex series of levees, dikes, and channels to control the river's flow.
The only dam on the Willamette's main stem is the Willamette Falls Dam, a low weir-type structure at Willamette Falls that diverts water into the headraces of the adjacent mills and a power plant.  The locks at Willamette Falls were completed in 1873.  Elsewhere on the main stem, numerous minor flow-regulation structures force the river into a narrower and deeper channel to facilitate navigation and flood control.The dams on the Willamette's major tributaries are primarily large flood-control, water storage, and power-generating dams. Thirteen of these dams were built from the 1940s through the 1960s to be operated by the United States Army Corps of Engineers (USACE), and 11 of those produce hydropower. Flood-control dams operated by the USACE are estimated to hold up to 27 percent of the Willamette's runoff. They are used to regulate river flows so as to cut peaks off floods and increase low flows in late summer and autumn, and to divert water into deeper, narrower channels to prevent flooding. In addition, a relatively small of amount of the water stored in the reservoirs is used for irrigation.
Detroit Dam on the North Santiam River is the second tallest dam in the Willamette River basin after Cougar Dam. It is 463 feet (141 m) high and stores 455,000 acre feet (561,000,000 m3) of water. Lookout Point Dam on the Middle Fork Willamette River, forming Lookout Point Lake, has the largest water storage capacity, at 477,700 acre feet (589,200,000 m3). The other 11 dams are Big Cliff on the North Santiam River; Green Peter and Foster on the Santiam River; Cougar on the South Fork McKenzie River;  Blue River on the Blue River; Fern Ridge on the Long Tom River; Hills Creek, Dexter on the Middle Fork Willamette River; Fall Creek on Fall Creek; Cottage Grove on the Coast Fork Willamette River, and Dorena on the Row River.A continuing controversy about these high dams involves Chinook salmon and steelhead blocked from roughly half of their historic habitat and spawning grounds on the Willamette's major tributaries. Unable to survive and reproduce as they once did, they have been "brought to the brink of extinction".  Endangered species listings and a subsequent lawsuit by Willamette Riverkeeper led to a plan to improve fish passage and other actions to help native fish recover in 2008. Since then, work has proceeded slowly, and the Corps, citing engineering difficulties and cost, may not meet the original agreed-upon deadline of 2023 for a system of effective remedies.Other major dams in the Willamette watershed are owned by other interests; for example, several hydroelectric facilities on the Clackamas River are owned by Portland General Electric. They include the River Mill Hydroelectric Project, the Oak Grove project, and the dam at Timothy Lake.
Output:
What structures are used to produce hydropower?