When URBANSWIM considers whether to hold or cancel a swim because of water quality, we use a combination of current water testing, recent weather and rainfall, historical water-quality data, tidal conditions, and the characteristics of the specific swim location.

One important factor is Enterococcus bacteria, which is commonly used as an indicator of fecal contamination in recreational water. Unlike some measurements that can be obtained immediately, Enterococcus testing requires laboratory processing and typically takes approximately 24 hours to produce a result. That means there is no way simply test the water immediately before a swim and know exactly what the bacterial conditions will be at race time. We have to look at the complete picture.

Rainfall and Tide Cycles

Rain can wash bacteria and other contaminants from streets, land and stormwater systems into surrounding waterways. For that reason, significant rainfall before an event is an important consideration.

When possible, URBANSWIM looks for one to two tidal cycles after significant rain before making a final decision. This gives the waterway time to exchange and disperse water and allows us to make a meaningful estimate of conditions after the rainfall event.

We also consider how much rain fell, when it fell, the intensity of the storm, and the location of the event. A short, light rain is very different from a heavy storm that produces substantial runoff.

Historical Water Quality Matters

We don’t treat every location the same way. URBANSWIM maintains an understanding of the water quality patterns at the locations where we swim and considers historical testing and past conditions when evaluating risk.

For example, Governors Island has historically tested well, which makes water quality there less of a concern than at some other urban waterfront locations. That doesn’t mean water quality is ignored—we still monitor conditions—but a rainfall event at Governors Island is evaluated in the context of what we know about that particular waterway.

When Would URBANSWIM Cancel?

A swim may be cancelled or postponed when the available information indicates that water quality may not be appropriate for recreational swimming. This could include:

• An elevated Enterococcus estimate

• Significant rainfall combined with conditions that increase runoff or contamination risk

• Water-quality estimates that are inconsistent with the location’s normal historical patterns

• Other known or observed conditions that could make swimming unsafe

Because Enterococcus results take approximately 24 hours, cancellation decisions have to be made in the absence of same-day laboratory results. Under these circumstances, we use the most recent available testing together with rainfall, tide cycles, historical data and other relevant information to make the most responsible decision we can.

Our goal is not to cancel swims unnecessarily. We understand that swimmers travel, train and plan their lives around these events. At the same time, when the available evidence suggests that water quality presents an unacceptable risk, we will choose safety over holding the event.

URBANSWIM’s approach is therefore not based on a single test or a single weather forecast. It is a location-specific, evidence-based assessment of the conditions leading up to the swim, with the health and safety of our swimmers as the priority.