Tales of Stream Monitoring Fun
Lake Accotink Park
Friends of Lake Accotink Park
Friends of Accotink Creek

Friends of Accotink Creek and Friends of Lake Accotink Park hold biological stream monitoring workdays four times per year.
Thanks to all the volunteers who have joined us for this important data-collecting activity!

Volunteers keep their social distance on their way to the creek.

December 12, 2020 Stream Monitoring:

We had a crew of a dozen volunteers today, and a day that had a foggy start turning to overcast but cool 50 degrees.

Over half our catch today was the common netspinners, a species tolerant of impaired waters. Over a quarter was aquatic worms, another too-common tolerant species. It was a bit encouraging to see that the next most common invertebrate was caddisflies, an invertebrate less tolerant of impaired water.

One rare find today was a Chinese Mystery Snail. This is an alien species, all too common in Lake Accotink, likely the result of home aquarium dumping. Despite their empty shells being common along the creek banks, we have never caught a live one. It was a surprise to note that this invasive species is a member of the gilled snail family, intolerant of low water quality. We caught none of the more common lung snails, so tolerant of low water quality their presence pulls the stream health score down.

Today we were testing the use of a 500 micron mesh net, as opposed to our usual 1/16th inch mesh. The finer mesh offers the advantage of allowing very few small invertebrates such as midges to slip through the net onto the exam table. However, that is also somewhat of a disadvantage, because it is actually easier to count those very small invertebrates by lifting the net.

Accotink Creek achieved its usual numeric stream health score of 4, down in the unacceptable range. Sediment caused by excessive runoff from paved surfaces is the major factor reducing invertebrate populations and impairing the health of streams in our region. See the tabulated results here.

Paved surfaces are the nemesis of Accotink Creek's benthic invertebrate population. Take advantage of financial incentives to become part of the solution with Conservation Assistance.

The rescuers scour the gravel bars and shallows for any stranded mussels.

November 15, 2020 Mussel Rescue:

On November 12th the USGS stream gauge on Accotink Creek in Wakefield Park topped out at just over 2000 cubic feet per second, just over the threshhold at which freshwater mussels will be pushed out of the streambed and stranded on the gravel bars. A larger than usual group of fourteen volunteer rescuers assembled by the dam and spent about three hours searching the gravel bars after the creek returned to its usual level.

The one-mile stretch downstream from the dam is the only part of Accotink Creek in which mussels are able to survive at all, the high volume of shifting sediment having gradually smothered the populations elsewhere.

We located eighteen mussels and returned them to safety in the deeper parts of the creek. This is not a large number, but each female mussel has the potential to produce hundreds or thousands of progeny over time. We located some of each of the three mussel species found in Accotink Creek, the Eastern Elliptio (Elliptio complanata), Eastern Floater (Pygandon cataracta), and Paper Pondshell (Utterbackia imbecillus.

See the rest of the mussel rescue photos here.

Read about our 2015 freshwater mussel biological survey.

Learn more about freshwater mussels.

Mismatched dueling helgrammites!.

September 12, 2020, Stream Monitoring:

The sky was overcast today, but the early morning drizzle stopped before we got started. The temperature hovered about 70. Masks and sanitizer all around contributed to covid19 precautions.

We had several younger volunteers today, all equipped with rubber rain boots. Their enthusiasm exceeded the height of their boots, however, and all ended up happily exploring the creek with overtopped boots filled with water.

An unusual find here today was a damselfly larva. We also had a higher than usual catch of five hellgrammites. Some of our younger volunteers couldn’t resist the temptation to see hellgrammites in gladiatorial combat. They were not disappointed when placing two hellgrammites together in the same partition got an instant and aggressive reaction. (We hope the smaller one survived.)

The rest of our catch today was dominated by the usual netspinners, midges, and worms, yielding a numeric stream health score of 3, well down in the unacceptable range.

See the tabulated results here.

June 13, 2020 Stream Monitoring:

We enjoyed good conditions for monitoring, with clear skies and temperatures in the mid-70's. Covid19 lockdown restrictions had been eased enough that we could cautiously come toegether for our session today.

The abundance of invertebrates was reasonably good, with 242 being collected with two settings of the net. As usual, quality of the catch was another matter, with the most abundant species by far being midges and worms, two species quite tolerant of impaired waters.

A rare find today was two caddisfly pupae. Being unfamiliar with their pupal forms, we were not certain to which family they belonged. Even more interesting was being able to observe as one of the pupae began to emerge from its case.

Accotink Creek achieved its usual stream health score in the mediocre range, a 4 on the scale of 0 to 12, far from the acceptable range. See the tabulated results here.

Link to more photos (Mayfly and slamander photos are from a different location, Van Dyck Park in Fairfax City)

Caddisfly pupa, a rare find

Forgot the tables - working on hands and knees.

March 14, 2020 Stream Monitoring:

We had a crew of 5 volunteers today. The weather was splendid for this time of year, sunny and calm with temperatures in the upper 50's. Having forgotten to pack our portable camping tables, we were compelled to spread the collection nets on the ground and get down on hands and knees to examine their contents.

We got rather poor results today, requiring four nets to achieve the minimum of 200 invertebrates. Each net was coated with a film of fine brown algae that obscured the few invertebrates we had collected.

Close to half the invertebrates were tiny midges, so small that they wriggled through the net. Too small to be practical to pick up, we had to count them where they lay on the sheet placed beneath the net. Accotink Creek received a poor numeric stream health score of 4 on a scale of 0 to twelve. See the tabulated results here.

Paved surfaces are the nemesis of Accotink Creek's benthic invertebrate population. All the runoff during rainstorms pours down stormdrains and shoots into the creek, scouring away the banks and smothering stream life in fine sediment. Take advantage of financial incentives to become part of the solution with Conservation Assistance..

Accotink Creek Creatures

A lament for aquatic invertebrates penned
by a Girl Scout who joined us for stream monitoring.

Her work challenges us all to care about Accotink Creek
and our fellow creatures who must live in it.


Plan now to volunteer again with others to preserve our oceans and waterways
on the second Saturday of the months of March, June, September and December!
See our Calendar

Earlier sessions

Back to our main Monitoring Page