I took our second 2010 water samples Friday, May 21, at 1 pm.  Here are the “preliminary” results:
#1        Dock                       below 10 cfu
#2        Cedar Fork Creek   81 cfu
#3        Booker Creek         181 cfu

Caution level is individual reading above 400 cfu, or average above 200 cfu.

Lake water temp: 25-27C,    77-80F

The SECCI clarity reading was again 38 inches, same as the April test.

While these readings are higher than our previous sample and somewhat above our long term average, they were all below any minimum thresholds for concern.  These samples were taken sooner after rainfall than I would prefer, but several more days of rain were predicted between then and the Memorial Day weekend.

The testing guidelines indicate that we should not sample immediately after a rainfall.  Tests taken then are less accurate for several reasons.  It takes 3-5 days for rainwater from our watershed to clear the system, and we sampled about two days after a rainfall.  That was probably the longest rain-free time we were going to have before the end of this week.

The pattern of readings is consistent with rain flushing a normal amount animal waste from upstream ground surfaces after a long dry period.  The water near the beach and dock is in the deepest and most downstream part of the lake, and anything entering the lake at the two main tributaries is going to be most dilute by the time it gets there.  We also have some springs in the lake further diluting anything that comes in from upstream. The specific bacterium we test for does not live very long in water.  It lives and grows in warm-blooded animals.   Whenever there is a sewage overflow, the numbers are a lot higher than these.  After several days of rain, the watershed surfaces should be washed clean and the risks we face then are more from erosion than from surface contamination.

It is probably a good idea not to be swimming too far upstream from the dock and beach areas while we are getting regular rainfall.  The lake itself is acting as a natural filter, so the downstream end of the lake, near the beach, is going to be the safest.  Stay out of the lake altogether after a hard “gully-washer” rain and remember to shower afterward. Although we do not test for it, it is logical to assume that any unabsorbed fertilizers probably follow the same pattern after rainfall.  An algae bloom is the normal consequence of that and we usually see one of those in June.

Chuck Henage
chenagemht@aol.com