Overview of Invasive Species

BOLPF’s plan for dealing with the threat of AIS is multi-fold:

1) Keep it out. We now have inspector coverage at the public beach from 7am to 8pm every day from the fishing opener until October 31. This is what the Clean Boats / Clean Waters program is all about and is currently organized by Bill Foreman. He does the hiring of paid inspectors and scheduling of volunteers to fill in the gaps.  

2) If #1 fails, find it early and contain it for eradication. Here is where our Lake Monitor program comes in. Run by Cindy Miller, this program assigns specific shoreline segments to volunteer inspectors, much like the adopt-a-highway program for highways. Inspectors are asked to cover their assigned areas at least every two weeks.

3) Finally, in the fall we employ professional help to thoroughly survey the entire littoral zone of the lake which takes the better part of two days. To see the summaries of those searches go to the Yearly AIS Search Results page and select the survey you’d like to see. 

Should any of these inspections find a form of AIS we have 4 fifty foot sections of heavy rubberized plastic containment curtains to encircle and isolate the infestation for the DNR’s Rapid Response team to take care of it. See photo:

So, exactly what are the threats? Ever heard of a Spiny Water Flea?  How about Curly-leaf Pondweed?   Zebra Mussels?   NONE of these are in Black Oak Lake.  Rusty Crayfish?  Those we have had for decades and they are rather benign, no doubt due to the low Calcium in Black Oak’s water.   The Wis DNR did a 2007 study of Black Oak’s Rusty Crayfish which is summarized in Rusty Crayfish in Black Oak Lake. They placed traps around the lake and found an average of 1.7 Rusty Crayfish per trap. A similar study on Trout Lake in Boulder Junction averaged 55 Rusty Crayfish per trap.

Of all the forms of AIS, the worst one to get is Zebra or Quagga Mussels. They attach to boat bottoms, propellers, dock legs, ladder rungs, gravel on the lake bottom, etc. They have razor sharp shells that can slice hands and feet. But their Achilles heel is their need for copious amounts of Calcium in the water which they need to build their robust shells. Whitewater Associates took water samples in August, 2011, from which they determined that Black Oak’s Calcium concentration is 6.5mg/L which is low for the suitability for the zebra mussel to grow its shell. You can go to the Smart Prevention website to view the lakes on which they have done the calcium threshold study at www.aissmartprevention.wisc.edu and click on the online mapping tool. It has an interactive mapping tool that shows susceptibility of lakes to zebra mussel invasion based on calcium concentrations. The model used seven studies that measured effects of calcium concentrations on zebra mussel development and growth. The value derived for the lower threshold of lake suitability to zebra mussels was 10 mg/L. The UWEX model presents three classes of suitability: (1) “not suitable” to zebra mussel invasion (<10 mg/L Ca), (2) “borderline suitable” (10 ≤ mg/L Ca ≤ 21), (3) “suitable” (> 21 mg/L Ca).

The pH also is a factor and the pH in Black Oak (7.82) is in the range for the zebra mussel to flourish (7.4 to 8.7) but the calcium is far more influential. This low Calcium content is probably the reason that our Rusty Crayfish population has remained so low.

Then there is Eurasian Watermilfoil (EWM). So far, we are free of that but our luck could very well run out. If you want to see how bad it can get take a short drive to Phelps and head north on Highway 17 just a few miles to the Big Sand Lake public landing. Look into the water at your feet and at the milfoil mats blocking in the docks to your right. And consider that a two-inch segment can start a whole new colony.

Eurasian Watermilfoil Invasion at Big Sand Lake, Phelps, WI

Floating mats of Eurasian Watermilfoil on Big Sand Lake in Phelps, WI.

The lighter colored parts of the floating mats are areas where it is so thick it is stacked up and drying in the sun. The stench is nauseating. Boats cannot penetrate these mats and must be routed through lanes that are progressively closing. Soon, many homes will be cut off from the main lake.

Underwater plant growth is important to the health of a lake in that it absorbs nutrients that are naturally present in any water body. Without a healthy absorber the nutrients will fuel algae growth, which clouds the water and reduces sunlight penetration. There are other types of milfoil (mostly Northern Milfoil) that are present in Black Oak Lake but, like all our other lake weeds, they die off in the fall and start over in the spring. The unique thing about the Eurasian variety is that it just keeps growing – even under the winter ice. This causes it to form surface mats that will stop boats and kill off most life below by stopping sunlight penetration. It also breaks off into free floating mats that drift to shore, rot in the sun, and exude a putrefying stench.

How quickly can an infestation spread? Lake Minnetonka in Minneapolis went from no detected EWM at all to the current status of five Milfoil Harvesters operating all summer long in just three years. This 14,500 acre lake has areas where the milfoil is solid all the way to the bottom in 15’ of water!

Milfoil Harvester

Is EWM just a waterfront owner’s problem? Not at all. Obvious economic victims of milfoil would be tourist sensitive businesses – which describe just about all the businesses up here. Less well known is the fact that 92% of the Vilas County tax base is the waterfront property. Pull up Lakeshore Property Values to see how property value varies directly with water quality. If EWM forces waterfront values down, the off-water properties would have to make up the resulting shortfall in property taxes. Another information-loaded site is:

Should EWM ever get started in Black Oak Lake it would not be the end of the world. If it is found early enough the plant(s) can be plucked carefully from the bottom and the site monitored closely in the future. Also, chemical treatment inside the containment curtain would be done. A buoy would keep boats away that might chop it up.  The reason EWM got out of hand on Big Sand Lake’s 1400 acres is that it was not identified for decades. By the time people realized what it was it was far too late.