text: The largest of these structures stretches half a mile and is located in the very remote Wood Buffalo National Park in Canada.
full_question: The largest of these structures stretches half a mile and is located in the very remote Wood Buffalo National Park in Canada. The construction of these structures has devastated Tierra del Fuego, because local flora aren't amenable to coppicing, and has led to one of the largest fauna eradication programs in history. Secondary ex- amples of these structures can provide counterpressure to shore up their primary structure or protect food caches. These structures are often designed to protect a "lodge" that's used for shelter. They're the original ex- ample of allogenic ecosystem engineering and are anchored by poles and branches set up parallel to a body of water's current and pointing upstream. For 10 points, name these structures that are created on streams by a large aquatic rodent.
first_sentence: The largest of these structures stretches half a mile and is located in the very remote Wood Buffalo National Park in Canada.
raw_answer: beaver dams [or beaver ponds until it is read; prompt on dams]