Sunday, September 5, 2010

Lake Pontchartrain water quality – is it safe for swimming?


As a child I grew up on the north shore of the Lake. I remember the Lake being so polluted that it was off limits to swimming. Though I lived all my life within an hour or the Lake, I never considered swimming in it until I registered for the inaugural Ochsner Ironman New Orleans 70.3 in 2009. The swim course for IMNO 70.3 is in the Lake so it’s not optional. Registering for the race made monitoring the pollution and water quality for swimming in the Lake a personal priority.
In 1979 the Department of Health and Hospitals posted "No swimming" advisories along the south shore of Lake Pontchartrain.
In 1989 the Lake Pontchartrain Basin Foundation began its work to restore the health of the Lake. By 2006 the Lake is removed from DEQ;s impaired water body list.
So how do you make an educated decision on swimming in Lake Pontchartrain? GNO Tri member Eric DeRonde summarized the decision process succinctly. “Open water swimming, just like biking in the rain and running with mp3 players, is all about risk assessment. Get the facts, assess the risks, assess your abilities, combine and make a decision.”

Get the facts.

The Lake Pontchartrain Basin Foundation takes weekly samplings of the water quality in ten locations surrounding the lake. The tests are taken on Tuesdays and their reports are published on Fridays on their website at: http://www.saveourlake.org/weekly-report.php

Here is a recent example of the Basin Foundation weekly report following a week of heavy rain:



This Week’s Numbers

Please note that Lincoln Beach is inaccessible
and Bayou St. John has replaced it for the time being.

This report is based on conditions found on the sampling day (8/31/10) only.

Date: 8/31/10
Fecal
Water
Water
Salinity
Disolved
#
Site
Coliform
Temp
Visibility
(ppt)
Oxygen


(MPN)
(F)
(feet)

(mg/L)
1
Laketown
49
81
n/a
1.8
7.32
2
Bonnabel Boat Launch
>1600
80.8
n/a
1.9
7.11
3
Old Beach
540
80.8
n/a
1.9
7.50
4
Pontchartrain Beach
920
81
n/a
1.9
7.12
5
Bayou St. John
170
83.1
n/a
2
6.04
6
Bogue Falaya
n/a
76.4
.82
0
6.41
7
Tchefuncte River
n/a
n/a
n/a
n/a
n/a
8
Bayou Castine
920
81
1.64
1.19
4.36
9
Fontainebleau Beach
79
81.3
1.64
1.3
5.87
10
Northshore Beach
49
81.9
2.46
4.9
7.05

 

The location number that corresponds with the “swim hole” is number 3 above, “Old Beach.” 

The count triathletes talk most about is the fecal coliform mean probable number (MPN). According to the standards set forth by the Louisiana Department of Environment Quality, swimmers should use caution when the fecal coliform MPN exceeds 200.Since I began to train for the New Orleans half-ironman distance race in 2009, I have swam in the Lake more than a half dozen times. Each time I swam the fecal count was below 200. 

The only times I have seen the count above 200 is after a lot of rain. As we in south Louisiana are at the height of Hurricane season, there is a lot of rainfall this time of year.  On the date I copied this table the fecal count exceeded the 200 MPN threshold at 540.

The high fecal count reading spawned a lively discussion on the GNO Tri* forum last week about whether it was safe to swim in the Lake. The scientific information and opinions shared were illuminating. It wasn't long before I knew it needed to be compiled so it could be shared.

So does a reading of 540 on Friday, mean it’s unsafe to swim on Sunday? That depends.

Assess the risks.

A snapshot in time. DeRonde notes that “the data on the website only shows the water quality right at the moment when the sample was taken. The data isn't valid for a week; it's valid for the 10 minutes when the sample was taken. That's it! It's very useful for long term tracking of water quality in the lake, but for making a decision to swim in it, it's really not all that useful.”

The role of rain and runoff. Rainfall runoff directly affects the Lake’s water quality. The Basin website warns that if it has rained in the past three days, the runoff could pollute the Lake.

DeRonde shared the following risk assessment for rain:
     No rain for a week: low risk
     Steady rain for 3 days: moderate risk
     Very heavy shower yesterday: high risk

Ecoli, shigella and staph, oh my! “The (infectious) worry about heavy run-off is mostly concern about exposure to sewerage – that’s that E coli count,” according to Dr. Susan McClellan with the Infectious Diseases and Tropical Medicine Department of Tulane University’s School of Medicine and a GNO Tri member.

E coli is a nasty bacteria, known by the low down bad company it keeps.
Though the mention of E coli conjures up disgusting images, we apparently track E coli because of the nasty company it keeps. Writes Dr. McClellan, “The E coli mostly won’t bother you (just an easy to measure marker), it’s the occasional diarrhea-causing Salmonella / Shigella / whatever that might also be in sewerage that you don’t want to swallow.  Of course some of those natural Vibrios can do it too.  Run-off or no, we share the lake with a lot of critters, some of which can occasionally do us damage."

What about Staph? According to Dr. McClellan, “If one gets a Staph infection from an injury in the water, it was probably bacteria colonizing one’s own skin that did it – Staph are not particularly water bugs.  There are plenty of water bugs which can cause a nasty wound infection (Vibrio of various sorts, Aeromonas, Pleisiomonas, Erysipelothrix, and the ever popular M. marinum, for example), but these are not related to any type of run-off or human pollutants or sewerage, they are normal inhabitants of wet environments (variability dependent on salinity, turbidity, temperature, etc but you get the idea).”

Assess yourself.

In addition to the water quality data and an understanding of the risks, you must add yourself to the equation before making an informed judgment. DeRonde suggests asking the following questions:

1. What is your sensitivity to foreign matter? Do you have an impaired immune system? “Some people have stronger stomachs then others. Some build up resistance, others not so much.”

2. Do you have any open wounds or abrasions? “If you have open wounds, dress them waterproof, or stay out of the water when risk is high.”

3. How strong of an open water swimmer are you? “If you can't breath very well yet in the waves and still take in gulps of water every third breath, then that's a risk factor.”
 
At GNO Tri's 4th of July practice triathlon, swimmers of all abilities took to the Lake for a swim.
Combine and decide.
The bottom line, as DeRonde points out is “there is no one single ‘the lake is safe’ or the ‘the lake isn't safe’ answer. Open water is never 100% safe, as there are always risks. Know your risk and use common sense. The question that needs answering before you jump in is: Are the risks present in the current conditions manageable within my capabilities?"

Coug and Lizzard (me) slither into our wetsuits for a Lake Ponchartrain cold water practice swim the day before the New Orleans half-ironman distance race.
Anecdotal accounts of infection are few, but still exist. GNO Tri member Keith Clement experienced the nastiness of an open wound infected by the Lake’s water. Last year after pulling his boat out from the Bonnabel boat launch he knocked his hand against the trim tab causing a brush burn.  Two weeks later a large cyst developed on his hand requiring two hand surgeries and months of antibiotics to fight the bacterial infection. “At my first appointment with the infectious disease doctor,” Clement recounts, “he said I was the 4th patient within the same week with the same bacterial infection (all water related).”  Did this infection keep Clement from swimming in the Lake? No. “There’s “stuff” anywhere you go, just use common sense and know your risk. I still fish the lake."

Nor has it kept the Dr. McClellan. “As someone who grew up swimming in the lake in its peak of contamination in the 60s, I’m a lot more afraid of inhaling a piece of plastic than most of the bacteria.” says Dr. McClellan. “So you play the game, you take your chances, trying to keep it within reason and your own comfort level.” 

Happy swimming!

* GNO Tri is an active tri club in New Orleans. GNO Tri is coached by Kevin Pilet and Rick Montgomery. Kevin and Rick are well respected in the tri community and all around great guys. Kevin and Rick host open water swim clinics periodically and are very gracious about allowing non-members participate.

4 comments:

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