The Swim Guide 411: The Ins and Outs of Water Quality Testing

Swim Guide 411: The Ins and Outs of Water Quality Testing

by Cece Pless, Communications Intern


Nobody likes to feel powerless, which is why we want to provide you with the information you need to be prepared for all kinds of situations in our watershed. Given the number of water quality tests that we have seen come back with numbers that are above the EPA threshold for safe swimming, we thought a refresher clinic might be helpful to keep everyone on the same page.

  • What is the EPA Threshold for safe swimming and why?

    • The EPA Threshold for safe swimming is determined by the number of "colony forming units" (cfu) per 100 milliliters of water. At 104 cfu/100mL, it is estimated that 3% of healthy adults will contract a waterborne illness. Any level below 104 is considered to be safe and any level over 104 is above the threshold for safe swimming.


  • Where does the bacteria come from? 

    • For Swim Guide, the bacteria tested (Enterococci) is associated with fecal matter that might be found in sewage or in waste washed into the water from an upstream source. Some examples might include: livestock, household pets, portable restrooms, and marinas. 


  • If Swim Guide is testing for Enterococci, what about other bacteria?

    • Swim Guide does not test for Vibrio Vulnificus or Escherichia coli. Vibrio Vulnificus is a flesh eating bacteria commonly found in warm, brackish waters and Escherichia coli (or E. coli) is another bacteria associated with fecal matter that is commonly found in fresh water. The best practice for avoiding exposure to Vibrio Vulnificus is to refrain from entering the water with open wounds. Additionally, it is always good to wait for at least 48 hours following heavy rain before entering bodies of water in order to avoid exposure to other bacteria contaminants.


  • Does Swim Guide test for Harmful Algal Blooms (HABs)?

    • Swim Guide does not test for HABs or other plant and animal activity, although it is important to note the affect these can have on water quality and in this case, safety. A Harmful Algal Bloom, commonly called a red tide, occurs when colonies of certain types of algae (a plant) grow out of control and produce toxins, which can be deadly to marine life and have been known to cause illness in people.


  • Are there other things I should be concerned about before swimming?

    • We always recommend following certain precautions to ensure your safety such as: swimming at beaches where a lifeguard is on duty, not swimming when a beach or swim site has a flag indicating that conditions are hazardous, and using a personal flotation device. Swim Guide’s purpose and Mobile Baykeeper’s mission in sharing this information is to inform you of water quality conditions at listed swimming sites.


  • If it doesn’t tell me everything above, what information is Swim Guide sharing?

    • Mobile Baykeeper uses Swim Guide to share water quality results from safe to unsafe; when the amount of Enterococci found at a swim site is found to be above the safe limit for swimming (according to the threshold defined above), the site is marked red.


  • What can you do around the water when it tests above the EPA threshold? 

    • Different levels of exposure (i.e. walking on a beach versus swimming in the water) will result in different risks. The safest recommendation is to use caution in all activities until water quality results come back within the safe limit, however the EPA and the WHO suggest that incidental contact (as with boating and fishing) does not encounter as much risk as with whole-body contact. Mobile Baykeeper exclusively uses the EPA threshold defined above for swimming to determine if water quality standards are “safe.”


  • How can you help keep water quality within a safe limit?

    • If you are doing construction, using proper fencing will help contain sediments.
    • If you have pets, making sure to pick up after them will keep their waste from washing into your backyard creek. 
    • If you use agricultural pesticides or lawn fertilizers, using them in moderation or choosing organic and natural alternatives can help prevent algae issues downstream.
    • If you own a boat, responsible disposal of your boat's sewage can make a significant difference in harbor water quality.

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