You’ve packed the cooler. The towels are in the car. Someone remembered the sunscreen (hopefully). The weather is perfect, and after a long drive, you finally arrive at the water, ready to swim, paddle, kayak, canoe, cast a fishing line, or simply enjoy a beautiful day outdoors.
Then you notice a sign:
Beach or Water Advisory
You pause.
Can we still swim? Is it safe to launch the kayak? Can the kids play near the water? Is this just a precaution, or should we come back another day?
If you’ve ever stood on the shoreline wondering what that sign actually means, you’re not alone.
Beach advisories are designed to protect public health, but they don’t always answer people’s questions. Water conditions can change quickly after heavy rain, toxic algal blooms can appear unexpectedly, and bacteria levels aren’t something you can see with your eyes. In fact, water that looks crystal clear does not mean it is safe for swimming.
That’s why a few simple resources can make a big difference before your next beach, boating, or fishing day.
Before You Go, Check First
Just as many of us check the weather before heading out the door, it’s worth taking a minute to check your local beach or swimming advisories before spending the day on the water.
Recreational waters may be monitored for two main health concerns: bacteria, most commonly E. coli, and toxic algae, also known as harmful algal blooms (HABs). Some blooms can produce toxins that make people and animals sick, so monitoring may look for both the bloom and the toxins it produces.
Bacteria: What You Can’t See Can Still Make You Sick
E. coli is used as an indicator that water may have been contaminated with fecal waste from people or animals. While not all E. coli are harmful, elevated levels can signal that other disease-causing germs may also be present.
Health officials collect water samples to determine whether E. coli levels are safe for different types of recreation. Not every activity involves the same amount of contact with the water. Swimming is considered total-body contact because your entire body may be submerged and you are more likely to accidentally swallow water. Activities such as boating or fishing generally involve less direct contact with the water and are considered partial-body contact. Since swimming involves greater exposure, the water quality standard is more protective for swimming than it is for partial-contact activities. Michigan uses both total- and partial-body-contact standards, and other states and provinces may use different standards or approaches.
One of the biggest reasons bacteria levels increase is rainfall. Heavy rain washes stormwater across roads, neighborhoods, parks, farms, and parking lots, carrying pet waste, wildlife droppings, agricultural runoff, and other contaminants into nearby lakes, rivers, and beaches. In some communities, heavy rain can also overwhelm sewer systems, allowing untreated wastewater to reach recreational waters.
The challenge is that water quality can change much faster than beaches or lakes are tested. A beach or lake that tested safe yesterday may have elevated bacteria levels today after a heavy rainstorm. Testing frequency also varies from place to place, and local health departments are generally responsible for monitoring beaches and determining when closures are necessary. That means a posted test result is an important tool, but it may not always reflect what has happened in the water since the sample was collected. That’s why it’s always a good idea to consider recent weather, even if no advisory has been posted yet.
Harmful Algal Blooms (HABs): Not All Green Water Is Safe
Bacteria are only one concern. Lakes, rivers, and beaches may also experience harmful algal blooms (HABs), which occur when cyanobacteria, sometimes called blue-green algae, grow rapidly. Some cyanobacteria can produce toxins that may make people and animals sick.
Unlike routine bacteria monitoring, HAB monitoring can be much more limited. In Michigan, for example, state agencies sample suspected HABs on a limited basis, and officials acknowledge that some affected areas may go undetected. Blooms can also move, disappear, reappear, and change within the same day. That makes knowing what to look for especially important, particularly during the warmer summer months when HABs are more likely to develop.
Since testing may not always capture a bloom as soon as it develops, it’s also important to know what warning signs to look for when you arrive at the water. Sometimes, harmful algal blooms are visible (Figure 1). The water may look like pea soup, spilled green or blue-green paint, floating scum, or thick mats on the surface. However, you cannot tell whether a bloom contains harmful toxins simply by looking at it. If you see suspicious algae or scum, the safest choice is to stay out of the affected water and keep children and pets away.
Figure 1. Avoid water with visible scum or unusual color. (CDC)
Staying Safe Starts Before You Jump In
Beach and water advisories aren’t meant to ruin a fun day outdoors; they’re there to help keep you, your family, and your pets healthy. While no single resource answers every question, understanding what advisories mean can help you make informed decisions before heading to the water.
Before your next trip to the water, take a few extra minutes to:
- Check for local beach advisories or closures.
- Look at recent E. coli water quality test results, if they’re available.
- Check for HAB advisories.
- Consider recent weather, especially heavy rainfall, which can cause bacteria levels to rise between testing events.
- Avoid water with visible scum, unusual discoloration, or signs of a harmful algal bloom.
A little preparation can help ensure your day on the water is remembered for sunshine, paddling, and making memories, not an unexpected trip to the doctor.
Note: The resources highlighted in this article were developed by trusted public health and government organizations and are shared as educational tools to help people better understand beach water safety. Given that monitoring programs and advisory practices vary by state and province, always rely on your local or state agency for the most current information about the water where you plan to recreate.
Not sure where to look? Beach advisories and water quality information are typically posted by local health departments, state health departments, state environmental agencies, state park systems, or other agencies responsible for monitoring recreational waters. Many provide online maps where you can check current beach conditions, recent water quality test results, active swimming advisories, and beach closures before you head out.
