Killin Wetlands Nature Park, which lies outside of Banks in Washington County, is one of the few remaining peat wetlands in the region, and up until this past spring, was most notable for the expansive ponded water forming a large wetland lake across the 641-acre nature park and natural area.
But earlier this year, the lake started to shrink.
Visitors who enjoy the park and natural area for walking and birding, and neighbors who drive by the wetland complex daily, certainly noticed. Metro received many calls from concerned visitors and neighbors wondering what changed the lake so dramatically in such a short period of time.
Was Metro letting water out of the wetlands, we were asked.
It’s a fair question. Metro controls water levels in Smith and Bybee Wetlands Natural Area to benefit plant and animal communities, and Metro often removes small dams from creeks in natural areas to improve water quality and fish and wildlife habitat. But not at Killin Wetlands.
We had a guess what was going on, but we wanted a clear answer as much as our keen-eyed visitors. Metro staff investigated on foot and using a drone and confirmed the suspected cause. Spring rains brought record water to the region and proved too much for the humble beaver dam complex that forms the natural “bathtub plug” of the wetland lake.
The beaver dams failed. A permanent water gauge in the wetlands indicate the failure likely occurred in spring 2022, when water levels in the wetland lake show a sudden drop.
It appears the beaver family maintaining the dams have either left the area, or the dams were simply not able to handle the unusually high-water levels of the growing lake.
The de-watering of the peat wetlands is concerning for a number of reasons. If the site remains dry, the slow process of peat soil re-building will pause and the peat basin will once again begin emitting carbon into the atmosphere rather than serving as a carbon sink. Drier conditions will permit the expansion of reed canary grass into the wetlands. Open water habitat that waterbirds use for breeding, wintering and migrating will be significantly reduced, and turtles and amphibians will have much less open water for cover and breeding.
So what do we do when a natural process (beaver dam failure) is threatening other natural processes? For now, we are in a waiting period to see if the beaver become active in the area and re-build. Longer term, we may explore options that lend the beaver a hand (or a paw?) by installing beaver dam analogs, which can assist dam formation by providing a solid structure on which beaver can build. Staff are monitoring the area to check for beaver activity and are consulting with the Oregon Department of Fish and Wildlife to determine if any further actions are needed.
Metro has worked for two decades to restore the peat wetlands at Killin. We won’t ever take for granted how much we have been helped by a beaver family that kept the hole plugged.