- Lake Forest Association (LFA) - Caretakers of Eastwood Lake in Chapel Hill, NC.
This year, we took a late season water test on October 3 at 9:45 am. The test results are as follows:
#1 Dock 17 cfu
#2 Cedar Fork Creek 1 cfu
#3 Booker Creek 11 cfu
Caution level is individual reading above 400 cfu, or average above 200 cfu.
Lake water temp ranged from 23C/74F to 23.5C/75F
The SECCI clarity reading was 42 inches on 10/3, 32 inches on 9/29. The rain gauge had 0.4 inches. It had 1.8 inches on 9/29.
This is very clear, the water in the sample bottles looked like drinking water from the tap, rather than the faint golden cast that our lake usually has. This is the second clearest we have had since we began monitoring turbidity around 1998/1999. As I have said elsewhere, clarity is unrelated to bacterial contamination….This just indicates that we are having very good water flow without a lot of erosion. On the 29th we had “level 2 flow” at the dam, on Oct 3, the day of the test, we had “level 1” flow. Steady water flow is good for flushing stuff out of the lake and maintaining good d.o. (dissolved oxygen) for the organisms that live in the lake.
The spillway has three steps, each of which is a couple of inches higher. Level 1 is about 4 feet wide, level 2 is about 48 feet wide, level 3 is the full width of the spillway, and level 4 is the full width of the dam. A level 4 flow is a raging torrent. We get level 3 flows regularly in spring, and we had a “surf’s up” level 4 flow during and after Hurricane Fran in 1996.
The water temperature is too cool for most swimmers, but we have had some hardy regulars in the lake, and the air temperatures have been mild. Where I grew up (Chicago) they opened the beaches on the 4th of July if the water was 70 degrees, so the range of acceptable temperatures varies by latitude.
Although the water is very clear, there is a lot of debris on the surface: leaves and stuff that looks like goose down. The breeze was cool and clear but very slight, and the still water was glassy between the clumps of leaves. Notably, there was almost no debris in the Booker Creek arm of the lake (left side when standing on the beach looking across at the gazebo). That was also the side with the slightly higher bacterial count. All of our readings for the past couple of years have been negligible. It might be helpful to know that these readings change logarithmically, since we are measuring something on the surface of a 3 dimensional volume of fluid. Orders of magnitude matter, so 2-20-200 is more important than 11-17. Part of the reason the EPA guidelines use e-coli is we can get these linear gradients that help us determine where it is coming from and how rapidly it is dissipating. In this case there as a slight bump, it came from Booker Creek, and it is decreasing, now mostly gone.
This test was requested because a couple of dead deer were removed from a location upstream of the lake, I believe on Booker Creek across North Lakeshore Dr. It takes a few thousand gallons of sewage to produce a noticeably elevated bacterial count in Eastwood Lake, which is about 52 acres with an average depth of 5-6 feet; 25-30 million gallons. 2 dead deer do not produce a lot of e-coli since it stops growing when they die, and most of it does not leak out. Not to put too fine a point on this, it is the poop bacterium.
Our testing is not often enough or precise enough to catch everything. If you see or smell anything worrisome, use caution. This is a natural ecosystem so things will poop in it and die in it. It seems to be fairly healthy. Our biggest risks are from the following: wastewater spills, agricultural (lawn and garden) chemical runoff, and erosion. Of these, the third one occurs naturally because of our soil type, but can be mitigated or made much worse by development in the watershed. Human activity influences all three issues, it is our job to protect this great resource.
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