Hannum Mill Dam

River/Stream: South Skunk River

Location: north of Ames, Story County
        Latitude: 42.068385
        Longitude: -93.619329
        Click here to view an aerial map of the dam.


Owner: U.S. Geological Survey

Height: 3 feet

Length: 50 feet

Hazards: drowning, varying

Warning Signs: standard signs in place

Portage: in July, 2018, the portage on river right washed out and is no longer complete. The bank is expected to continue eroding towards the dam as water is swirling in this area. The portage trail has been fenced off. Three large trees are down in the river near the dam.

Comments: ruins of very old rock crib mill dam capped with concrete; also known as US / General Filter Dam

Incident Report:

"The accident occurred at what we call the US Filter dam, just north of Ames & almost visible from Hwy 69 opposite Ada Hayden Park. I'd say it's a 3-4 ft drop at most levels. It is obvious as you approach from upstream & is routinely run by canoes, kayaks, and tubers, but for those that choose to use it, there's an EASY portage river-right accross the dam structure itself.

"We're told that the concrete structure caps the original rock-and-crib mill dam, and that the four large timbers sometimes visible on the downstream side are part of the original cribbing. The concrete cap has a sloping downstream surface but does create a small hydraulic at it's base.

"I think it's fair to say that as low-head dams go, most of us never considered this one particularly dangerous. I suspect Tom had run it before on numerous other occasions. I don't know if the hydraulic could have been a factor, but it is easy to imagine someone swamping as they scraped across the dam (the water was relatively low on the 17th) or hit a standing wave or timber at it's base. Capsizes here are not uncommon."

Fatalities 2

  • April 17, 2005 - canoeist Thomas Manatt
  • May 3, 1963 - floater David Barnhart

Overlook of dam from southern bank

Looking downstream over dam horizon line