Many
times during the summer months, when Madison residents choose to go swimming in
their local lake, Lake Wingra is closed due to high levels of bacteria, most
commonly Escherichia coli (E. coli). Vilas beach is the most used beach in the
Madison area, and is the location of many recreational activities (Friends of
Lake Wingra, 2007). There could be many sources contributing to the high levels
of E. coli in Lake Wingra, but the large numbers of waterfowl (Canada geese)
around the lake are most likely a major contributing factor (Lorman, 2003).
Samples of water are regularly taken from Lake Wingra during
the spring and summer seasons by the Madison Department of Public Health. They
test the water for coliform bacteria including the most common species, E. coli,
and if the levels are too high they close the lake to protect the health of
swimmers. During the colder seasons, bacteria tests are not needed due to the
fact that the lake water will not be used for recreation (Beach Monitoring
Program Requirements). Our goal was to compare our bacteria tests conducted in
winter with those in the warmer seasons to determine if there was any
correlation between bacteria levels and the time of year. We also wanted to
determine if E. coli levels were different in various locations around the lake.
Based on our background research, coliform bacteria can enter
the lake in many ways. It can come from birds (most likely geese) and household
pets, leaking sewers, storm water runoff or nearby farms. E. coli specifically
is found in the lower intestines of mammals, and dangerous strains can cause low
red blood cell counts (hemolytic anemia), low platelet counts
(thrombocytopenia), and kidney damage (renal failure). Symptoms of an E. coli
infection include: fever, nausea, vomiting, diarrhea, and cramps (Escherichia
coli, 2007).
The state of Wisconsin’s Department of Natural Resources has
specific criteria for sampling, monitoring, reporting and notifying the public
of E. coli levels in lakes. Beaches are designated as a high, medium or low
priority beach based on the number to people who frequent the beach and the
potential for fecal contamination. Depending on the beach’s priority, when basic
sampling should be conducted, when additional samples should be taken and where
and how to collect the samples vary. Notification including beach advisories and
beach closures remain the same for all levels of priority. Advisory signs must
be posted whenever the level of E. coli in the beach water sample exceeds
235cfu/100ml (Colony Forming Unit/ml, CFU and Most Probable Number, MPN can be
used interchangeably). If a beach water sample exceeds 1000cfu/100ml, all
beaches must close. Additionally, beaches will be closed when there is a
reported illness due to the lake, after a major pollution event or after a
significant rainfall. Beaches can be re-opened when a sample is taken that is
below the established criteria (Beach Monitoring Program Requirements).
We sampled E. coli and total bacteria levels at four sites in
Lake Wingra once a month from November to February, and compared our results
with previous records as well as samples taken during the summer. We sampled
water from the Vilas beach, the Vilas lagoon bridge, the Edgewood pier, and the
Wingra Park. We hypothesized that the total coliform and E. coli levels would be
lower in the colder months due to:
• Colder water temperatures
• Fewer people and pets around the
lake
• No rainfall to carry bacteria from
the geese into the lake
Also, we predicted that the total coliform and E. coli levels at the bridge site
would be higher than at the beach because based on our prior knowledge of the
location of geese and a lab we performed first semester, there are more geese by
the bridge.