FRESHWATER SOLUTIONS PREVENTION STRATEGIES
SWIM AFTER LUNCH
FWS/UA scientists were able to quantify the risk of contracting swimmer’s itch as a function of time-of-day (Rudko et al. 5, 2018). Since most of the itch-causing cercariae exit the snails in the morning and only live for a day, you would expect fewer cercariae to be around in the afternoon due to movement by wind, predation, natural mortality, etc. FWS/UA documented that riparians greatly reduce their risk of being exposed to virulent cercariae as the day progresses.
SWIM WITH OFFSHORE WIND
FWS/UA scientists were able to show a strong correlation between wind direction (onshore, offshore, alongshore) with cercariae concentration (Rudko et al. 5, 2018), with significantly higher concentrations found with onshore winds.
ADJUST SWIM LOCATION
Results from work done in 2018 (Project ’18 Final Report6) show cercariae numbers increasing near shore with an onshore wind, with very high numbers found within 1 meter from shore. Very few cercariae were found in deeper water when samples were taken at regular intervals on a straight line transect from shore to deep water with either an offshore or onshore wind. Some find relief by traveling to and swimming in nearby waters where the parasites are absent or greatly diminished. Others find blow-up kiddie pools placed down by the water an acceptable alternative for infant to 3-year-olds.
WEAR A RASH GUARD
Rash guards are tight-fitting one or two-piece swimsuits fashioned from combinations of polyester, nylon, lycra, or spandex for stretch, breathability, and quick-drying properties. They are relatively inexpensive and protect against most water-borne invaders, including the cercariae that cause swimmer’s itch. Rash guards remove the need for creams and/or sunscreen (except to face), which eliminates foreign chemicals being applied to skin or added to the water. Additionally, rash guards work against all species of parasites.
INSTALL A SWIM BAFFLE
FWS/UA scientists innovated and conducted research on this prevention strategy in both 2017 and 2018. Results were very promising at multiple study sites and reduced risk by 90+ percent (Project ’17 and ’18 Final Reports6,7). Different configurations were tested and optimized. The biggest advantage is in creating a safer swim area for multiple riparians (such as a public beach or popular swimming beach). Improvements can be made to lower costs, improve appearance, and increase effectiveness if additional funds become available.
EMPLOY A PARASITE SKIMMER
FWS/UA scientists created and conducted research on this prevention innovation in both 2017 and 2018 as well (Project ’17 and ’18 Final Reports6,7). Since cercariae are mostly shed from snails in the morning and travel to the surface for the rest of the day, most can be easily “skimmed” off the water surface before swimming, similar to skimming leaves from a pool. This technique can be employed alone or in conjunction with a swim baffle.
TRAP AND RELOCATE COMMON MERGANSERS
This technique has the potential to impact the largest number of riparians on a lake. Effectiveness data are conflicting, with a couple of Michigan lakes reporting some prevention success while others are abandoning this technique due to minimal, if any, improvement. This technique requires costly initial assessment to obtain a nuisance permit from the MDNR and costly brood removal each year. Some associations are questioning the ecological impacts of removing an entire population of top-tier predators from a lake ecosystem; more study needs to be done in this area. Positive results take at least a year before they are realized. Research conducted by FWS/UA scientists in 2019 shows spring and fall migrants play a significant role on some lakes, making this technique less effective (paper in progress). Recent research shows relocated mergansers travel great distances from their release sites and swimmer’s itch is now being reported in the Great Lakes near release sites. Additionally, some relocation sites show cercariae in the water (Relocation Site Analysis Final Report 20198), which brings into question the sustainability of this technique.