Monthly Archives: September 2017

New Zealand Mudsnails

IMG_3156A population of New Zealand mudsnails (Potamopyrgus antipodarum)has been confirmed by Maryland DNR in the following press release. Thanks also to Scott Dance for early coverage in the Baltimore Sun of the prescence of the invasive New Zealand Mudsnails in the Upper Gunpowder River.

There are two schools of though on invasives; one is the “aw shucks” approach to let thing be, the other more conservative approach is apt to slowing the spread of invasives by educating river users and taking steps to containing invasives to the affected waterbodies. The good folks at MDDNR should be applauded by taking the conservative approach of letting angler’s know about this new invasive species of concern.

“We’ve been dealing with Didymo or “Rock Snot” an invasive algae in these waters since 2008. Initially the Backwater Angler shop maintained wader wash stations and in 2010 Gunpowder Riverkeeper took over maintenance of the stations with volunteers. Anglers are the vectors. We have anglers that fish globally. The Gunpowder is a nationally recognized wild trout fishery and made Field and Streams Top 5 tailwater or dam controlled rivers list in 2005. Whether it came from the Madison or Spring Creek is immaterial at this point. The only other known area on the East coast is Spring Creek in Centre County, PA. The Centre Daily covered the occurrence back in 2013.
Invasive species tend to inhabit disrupted ecosystems. It is widely known that the Gunpowder system has too many nutrients namely Phosphorous and Nitrogen that can be contributing to their abundance. Once established, New Zealand mudsnails can amass in such large quantities at over 300,000 per square meter. At these levels they are best described as biofoulers-like zebra mussels and are known to clog water intakes. Something to consider given that the Gunpowder River supplies water regionally to 1.5 million residents in the metro-area.

Because the snails are very hardy and temp, turbidity and salt they could move quickly into the rest of the Gunpowder system well below Loch Raven. Gunpowder Riverkeeper advises all visiting boaters and anglers to take precautions to clean check and dry their gear including physical methods like soaking gear in hot water or freezing gear before and after visiting the Gunpowder to reduce the chance of spreading invasive species.

Recent literature from the Oregon State indicates that New Zealand Mudsnails can also adapt to high salinity environments. Here is the USGS take on these critters that also includes a distribution map.

Finally, here is guidance hot of the press from MDDNR on cleaning protocols.After fishing in the Gunpowder Falls, at least one of the following decontamination methods should be completed:
Soak waders, boots, and equipment in a bath of 20 g/L Virkon Aquatic for 15 to 20 minutes. Spray application alone is not a reliable method of disinfection.

· Soak waders, boots, and equipment in hot water (>60oC) for at least 5 minutes (Not recommended for Gortex).

· Freeze waders, boots, and equipment for at least 6 hours at -3oC.

· Dry waders, boots, and equipment completely for at least 48 hours.


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Theaux M. Le Gardeur

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Late September on the Gunpowder


The Gunpowder is at 33 cfs and starting the day cold at 50 degrees at Falls road. The flows continue to be low for this time. However the past week the flows have been steady and with ideal water temperatures the fishing can be good, fish will always be opportunistic at this time of year. Caddis, around size 18, have been hatching in the afternoons through the evening from falls and the fish key in on these when happening. In the evenings, from the dam down to bunker hill area, tiny cream midges are hatching that are around size 24. Small subsurface patterns like Zebra midges, patterns for caddis pupa and small nymphs will do well in the riffles and fast water.