Search for Eurasian Water-milfoil on Black Oak Lake 2017
Susan KnightOctober 2017
A small group gathered on Walt Bates’ pontoon boat and searched for,but did not find, any aquatic invasive species on Black Oak Lake on 5 October 2017. Our team includedWalt Bates, John Annin, Bill Foreman, Joe Beersand me.The water was somewhat turbid and I used the Aqua Viewer constantly. The water was noticeably less clear than in other years and I could not see much more than about 7-8’ into the water. For this reason, only the shallowest parts of the lake were screened.
Many lakes are experiencing reduced clarity with all the rain we have had this year. In an analysis of lakes in high and low rain years, the authors found that lakes with the highest clarity are likely to experience the largest decline in clarity, while low-clarity lakes will experience a smaller change. This is logical, since a lake with low clarity cannot get much worse, and so the change due to increased precipitation cannot affect it to such an extent as a clear lake. The rain likely has a negative effect on lake clarity for two reasons. First, more of the watershed is in contact with the lake in a wet year, and so more nutrients will be carried from land to the lake. Second, the near constant rain is causing some turbulence near shore, decreasing clarity.
We crisscrossed the west bay and Barber’s Bay, but otherwise did one pass along the north and south shores. We were able to coverall the visible parts of the lake in just one day. As in other years, we found some EWM look-alikes, including northern water-milfoil, water marigold and alternate-flowered water-milfoil. We found plenty of other native plants indicating a healthy plant community. We did not find any exotic invasive species.
Almost every year, I see some large purple bladderwort (LPB, Utriculariapurpurea) in the west bay. Over the last two years (2015-2016) I have seen an increase in the density and frequency of LPBin the far west end of this bay. However, the LPB was much more abundant in this area this year than in any other year.LPB can become so abundant in some lakes that it reaches nuisance levels. 2017 seems to have been the year for large increases in LPB regionally, as I have had many reports from Vilas and Oneida County lakes about nuisance levels of LPB. However, unlike many lakes, where LPB often forms floating rafts and can interfere with recreation, LPB in the west bay of Black Oak Lake remained on the bottom and was not rafting on the surface.
Since the part of the bay with the dense LPB is very shallow, even an abundant bladderwort population might not make much difference to how this part of the lake is used and perceived by the home owners. This plant does not have any roots, and it is unlikely to persist in any other part of the lake where it would be quickly windrowed onto shore. LPB is most common in small lakes, with little fetch, and the plant is generally restricted to the edges of the lake. BOL is of course not small, but that bay is so different from much of the lake that it acts more like a separate small lake. It is possible/likely the LPB came in from neighboring George Lake where it is also abundant. Much to the chagrin of many lake residents, there is nothing to be done about the high density of LPB.
There was no need to canoe the shallow areas of the west bay or parts of the northwest shore as the lake level is high and easily accessed by the pontoon boat. The common bladderwort (Utricularia vulgaris) was also common and already had fully developed turions, or winter buds that look like miniature green boxing gloves.
Barbers Bay is probably the part of the lake most vulnerable to invasive plants for several reasons. Winds are often out of the west, so winds could potentially carry invasive plants from the landing (where they are most likely to originate) toward Barber’s Bay. This bay has a rich diversity of native plants, which is good and bad. With such a density of natives, there is perhaps less “room” for an invasive plant to find space to root. However, the high density and diversity also means that aquatic plants are successful there, and likely EWM would be successful too, given a chance to get started. As noted earlier, we traversed this bay more than other areas to be as sure as possible it was free of any invasive plants.
One good thing about the high water levels is that there is little chance that we will see any of the increasing numbers of invasive shoreline plants, such as European marsh thistle, that seemed to proliferate on sandy shores when the lake levels were low.
It is critically important that everyone involved in the Clean Boats Clean Waters and the Vigilante program remain alert to invasive species throughout the open-water season.Everyone remembers the 2015 event when the dock removal team tried to get onto the lake laden with EWM. Your vigilance is paramount!Remember to watch for EWM along the shoreline as well as in the water, since EWM, should it ever occur, will likely fragment and wash upon shore. Good work everyone, and see you next year.