Spring water flow arrives at historic Smith Ditch — and so do the crawdads

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Here’s a pleasant spring activity: staring into a ditch. Smith Ditch in Washington Park, to be exact.

It is easy to develop a crush on this little stream. If you pause on one of the footbridges, you may discover there is something gently hypnotic about flowing water.

Not only is it soothing to stare at, this prosaically named 154-year-old irrigation canal played a vitally important role in Denver’s history. Without it, we would have no trees, grass or flowers, and Denver would bear a strong resemblance to the surface of Mars.

It was brought to us by John W. Smith, the same 19th century entrepreneur who created Smith Lake by diverting his irrigation canal into a buffalo wallow on the arid scrublands. Hand-dug by shovel and horse-drawn plow in the 1860s, the canal diverted water from the Platte River, ran for 25 miles and transformed a city in desperate need of water. Colorado ranks as the seventh driest state in the nation, according to the Colorado Encyclopedia website, with a mere 15 inches of average annual rainfall.

In the panorama of history, Smith Ditch is only a recent example of the ancient art of irrigation, introduced to the American west by Native Americans a thousand years ago. Worldwide, irrigation dates back to at least 6,000 B.C. and gave rise to many great civilizations.

Today the ditch that gave rise to Denver is listed on the National Register of Historic Places, thanks to local preservationists who managed to save the old canal after it was threatened by highway expansion in the 1970s. The only remaining open section ripples through Washington Park. This generous little stream fills all the lakes in the park — Grasmere, Smith and the Lily Pond — before it plunges underground and travels north to water the Denver Country Club and top up the lake in City Park.

Another nice thing about the ditch: it ushers in spring. The canal is empty of water from November through March, its sandy bottom bare and exposed. All that changes at 8 a.m. on April 1 each year, when automated butterfly gates flip open at the small brick de-chlorination plant behind the playing fields at South High School. Water gushes from the pipes and finds its way under the park’s southernmost footbridge.

And just like that, a small and charming aquatic environment comes back to life.

Soon waterweeds sprout from the stream’s sandy bottom and dried sedge along the banks turn green. Blue and emerald dragonflies flit among the reeds and water striders scoot across the surface.

As any 5-year-old will attest, June brings the most exciting development of all — the arrival of the crawdads. Once the water temperature in the ditch warms up to 60 degrees, it entices those little freshwater lobsters out of their burrows. And that’s the signal for the kids to wade in. Netting crawdads and watching them crawl around in your bucket is a time-honored Wash Park tradition.

Some parents worry about water quality in the ditch, particularly because the city switched to using recycled wastewater in 2004. But that water is purified to a high standard, according to Ty Schmittel, a facility manager with Denver Water. First treated at the utility’s York Street plant, the recycled water is further purified at the `Dechlor Plant’ to one notch below drinking water.

Since crawdads will not tolerate polluted water, their presence in Smith Ditch is a reassuring sign. Scientists view them as a sentinel species and study them to monitor environmental health.

Often called “crawfish,” they are officially known as “crayfish,” which derives from their French name, “ecrevisse.” But it is more fun to call them `crawdaddies’ and `mudbugs,’ as affectionate Cajuns do just before popping their local red variety into the gumbo pot. Closely related to lobsters and crabs, these freshwater crustaceans have been crawling around on the bottom of lakes, swamps and streams since the Paleozoic era, well before the dinosaurs appeared.

If they were enlarged to a gigantic size, crawdads would make great sci-fi movie monsters. They are equipped with armored exoskeletons, eyes on moveable stalks, ten segmented legs and big front pincers. But in reality, most crayfish are too small to menace anybody — except minnows, snails and other male crayfish during courtship season. American species average only three-to-six inches long. While handy for tearing off a piece of waterweed, their lobster-like front claws are no threat to humans.

In fact, these nocturnal creatures spend much of the day hiding, since everything from hungry racoons to Cajuns seems to find them delicious. Bass love them — and so do bass fishermen, who use them for bait.

When threatened, the hapless crawdad does have a couple of tricks up its carapace. It can jet backwards by quickly curling and uncurling its fanlike tail. And if something big and hungry grabs one of its legs, the crawdad will bid that leg a fast goodbye and self-amputate.

How do they do it? Close inspection of their legs reveals thin horizontal grooves known as fracture planes, which are designed to snap off without any serious injury. A membrane quickly closes the wound and eventually a new leg grows in.

Another sci-fi thing about crawdads — they eat their own shells. Like growing kids, their outerwear frequently gets too tight. After molting — shedding the old shell — they need a big dose of calcium to grow a new one. And, of course, there just happens to be a large crunchy helping of calcium-rich exoskeleton nearby.

Crawdads are not native to Colorado. In the 1950s, Northern Crayfish from the Great Lakes region — which is a thousand miles away — started turning up in Colorado rivers. No matter how they got here, crawdads certainly make ditch-gazing a lot more fun.

As the water cools in October, crawdads begin burrowing into the banks of the ditch. Since they are aquatic animals who breath through gills, they need to dig down two-to-three feet, far enough to reach the water table.

They seem to sense what’s coming.

On Oct. 31, Denver Water turns off the tap and Smith Ditch goes dry for the winter — a precautionary move which prevents ice bridges from forming and causing the ditch to overflow.  

That makes winter a quiet time for crawdads and a sad time for ditch-gazers. All we can do is transfer our affections to Washington Park’s three beguiling lakes — until water begins flowing through the ditch again next spring. 

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