Navigating the Healthy Swimming Mapper

The Healthy Swimming Mapper from the New Hampshire Department of Environmental Services is a great way to stay up-to-date on cyanobacteria activity in the state. The map displays areas where cyanobacteria blooms and fecal bacteria have been reported, with different symbols to represent the identified level of risk. While it’s a great informational tool, navigating the mapper can be a little confusing at times. This guide is intended to help users use and understand this mapping tool.

Reading the Symbology

The pop-up explains what each symbol represents. Cyanobacteria activity is shown with triangles, while fecal bacteria data are displayed using upside-down teardrop-shaped pins. Reading through the pop-up provides a great overview, but it’s also important to know how to take action based on the map.

To understand the three triangles used to show cyanobacteria blooms, and what they mean for recreation:

• Black triangle: NHDES received a bloom report from a member of the public and was able to identify a cyanobacteria bloom from the report photos, but hasn’t collected a sample. There is no way to gauge cell density and determine the risk level from photos. If a black triangle is present, exercise caution in the area. Look before you leap, and don’t enter the water if it looks unsavory.
• Orange triangle: A bloom was identified, and a sample was collected. The cell density was approaching but did not exceed the safety threshold of 70,000 cells/mL. A watch will be issued, but unless there are further bloom reports submitted, the watch will be lifted after one week, and NHDES will not resample the location. If an orange triangle is present, perform a visual assessment and avoid contact with the water anywhere bloom material is observed. If the bloom persists past the date of an issued watch, please fill out the bloom report form to keep conditions current.
• Red triangle: A bloom was identified, and a sample was collected. The cell density exceeded the safety threshold of 70,000 cells/mL. A warning will be issued if the cell density exceeds the safety threshold at multiple locations. When a warning is issued, NHDES will return to sample the location in one week. Continue to perform visual assessments, and keep children and pets out of the water if any bloom material is present.

Note: Cyanobacteria blooms are dynamic and can move with wind, waves, and boat action. A triangle will be placed at the location where the bloom was identified, but that doesn’t mean the bloom will stay there. Make it a habit to take a look at the water before entering or letting pets in, as blooms can form or shift unexpectedly.

Moving Around the Map

To look at a certain water body, you can pan around the map on a computer by clicking and dragging. Zoom in and out with the buttons on the lower right side of the map, or with the scroll wheel of your mouse.

**Example results, check the Healthy Swimming Mapper for up-to-date information.

Reporting a Bloom

If you suspect a bloom, please report it to NHDES using the Bloom Report Form. Even if there is already a current watch or warning on the water body, making a report can help track the movement and persistence of cyanobacteria, especially if it has been days since the watch was issued and the bloom has continued or moved.

Here is a handy flow chart for encountering a cyanobacteria bloom:

Fecal Bacteria Advisories

The Healthy Swimming Mapper also displays the location of beaches that are regularly monitored for fecal bacteria in NH. If the tag for the beach is green, like in the bottom left photo, there are no current fecal bacteria advisories. If the tag is red, that means a fecal bacteria advisory has been issued by the NHDES Beach Inspection Program. Both red and green symbols can be clicked on for further detail, such as when the last sample was collected, as can be seen in the bottom right photo. None of the beaches are sampled every day, so NHDES recommends being cautious and avoiding swallowing any water.