The Johnston Brief
Saylorville is a flood-control reservoir on the Des Moines River, and its dam sits right in Johnston, run by the U.S. Army Corps of Engineers. When you want to know how high the river is, or how much water they are letting out of the dam, here are the official live gauges.
The live reading loads from the USGS gauge. If it does not appear in a moment, tap the official gauges below for the current numbers.
Every number here comes straight from the government agencies that run the river. Bookmark whichever one you need.
Flow, in cfs (cubic feet per second): how much water is moving past the gauge. One cfs is roughly a basketball of water going by every second, so a few thousand cfs is a lot. This is the number that really tells you how much the dam is letting through, and it is what the badge above is based on.
Gauge height, in feet: how high the water surface sits at the measuring point, measured above a fixed local zero. It rises and falls right along with the flow. Two things to know: it is not "how many feet deep the river is," and you cannot compare it between different gauges, since each one has its own zero point.
The National Weather Service does not publish a "flood stage" for this spot, because it sits right below the dam where the Corps controls the releases. So the honest way to judge high vs. low here is the flow: normal releases run about 200 to 6,000 cfs, and that is the range the badge compares against. For actual flood warnings, use the downstream Des Moines gauge and NWS links.
Saylorville Dam exists to hold back floodwater. When the Des Moines River runs high upstream, the Corps keeps releases low and lets the lake rise, storing the flood so towns downstream, including Des Moines, get some relief. When the danger passes, they let it back out. That is why the lake level swings so much through the year: it is doing its job.
Normal releases run between about 200 and 6,000 cfs through a gated conduit at the base of the dam. In a serious flood the outflow can go much higher: the record releases came during the floods of 1993 (about 47,100 cfs) and 2008 (about 60,600 cfs).
People often ask how much is going "over the spillway," but day to day the water leaves through the conduit, not the spillway. The emergency spillway is a separate structure that only comes into play in extreme floods and has rarely run. So the number you usually want is the conduit outflow, which the Corps reports on the Rivergages gauge above.
When the river is low, it is a fine time for the Saylorville beach, the marina, and shore fishing, though very low water can leave some boat ramps short, so check ahead. When it is high and the Corps is releasing hard, low-lying trails and parks along the river below the dam can flood first, and that includes stretches of the Neal Smith Trail near Johnston. For actual flood watches and warnings, use the downstream Des Moines River gauge, which does carry official action and flood stages.
Below the dam in Johnston, the Des Moines River runs past a string of access points on its way through the metro. Whether you find an exposed sandbar or beach at any of them comes down to one thing: how much water is coming through. Low flow uncovers the sandbars; higher flow covers them, speeds up the current, and can put the ramps underwater.
There is no official chart that says "a beach appears at X cfs" at a given ramp, so we will not invent one. The honest way to judge it: sandbars are best at low water and disappear as the river fills, so watch the flow and the badge above (and the downstream gauge below). A high-end or "running high" reading means the sandbars at Prospect Park, Sycamore, and the rest are mostly covered; you want low water for good exposed beach.
Ramps close for high water, ice, or construction, and Sycamore has been closed before for dangerous currents and repairs, so check Polk County Conservation or the Iowa DNR before you haul a boat. The closest official river gauge to these ramps is the USGS gauge downtown at 2nd Avenue.
When the river, the weather, or anything else in Johnston is worth knowing, the Johnston Brief has it, in one short weekly email.
The U.S. Army Corps of Engineers (Rock Island District) sets the outflow at Saylorville Dam, which sits in Johnston. Normal releases run between about 200 and 6,000 cubic feet per second (cfs), through a gated conduit, not the emergency spillway. You can see the current release on the Corps' Rivergages gauge for the Saylorville tailwater, and the river flow just downstream on the USGS gauge near Saylorville.
Saylorville Dam is in Johnston, Iowa, at the south end of the reservoir. The Corps project office and the lake's visitor center are there too, at 5600 NW 78th Avenue, so the dam and the gauges below it are right on Johnston's doorstep.
Day to day, Saylorville releases water through a gated conduit at the base of the dam. The emergency spillway is separate and only comes into play in extreme floods; it has rarely been used. So when people ask how much water they are letting out, the number they want is the conduit outflow, reported by the Corps.
The National Weather Service posts river forecasts, including predicted crests, on its water prediction gauges for the Des Moines River at the Saylorville tailwater and downstream at Des Moines. The USGS also shows real-time gage height and flow. Links to all of them are on this page.
Check the live gauges. The USGS gauge near Saylorville and the National Weather Service forecast gauge show the current river level against action and flood stages. This page pulls the current flow below the dam live from USGS, and links the official forecast gauges so you can see whether levels are rising or falling.
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