The USGS monitors the flow of the Siletz River at a station east of Siletz and from the mouth. The average flow of the river at this station is . This is from a drainage area of , or about 54 percent of the total Siletz River watershed. The maximum flow recorded there was on November 28, 1999, and the minimum flow was on September 5–6, 2003. Tides affect the flow along the last of the river.
