Water Temperatures: Summer 2016 was among the warmer summers in recent years. From June 18 to August 15 the average water temperature was 74.0˚; this compares to 71.4˚ in 2015. Looked at in 2-week increments, water temperatures increased steadily from a mild June through an exceptionally warm August: June 18-30 = 69.5˚; July 1-15 = 72.6˚; July 16-31 = 75.6˚; Aug 1-15 = 78.1˚. High recorded water temperature was 80˚ on August 15.
Swimmer’s Itch: Swimmer’s itch data from 2016 were largely consistent with findings from recent years.
- Overall, for 51 days from June 18-August 15 there were no reports of itch on 36 (70.6%). This compares with 74% of days with no itch in 2015, 53% in 2014, 67% in 2013, and 64% in 2012.
- Onshore (northerly) winds were reported on 21 days (41.2%); these days accounted for 80% of all days with at least one reported case (12/15) and 100% of days with 10 or more reported cases (7/7). There were reports of itch on 57% of onshore wind days (12/21).
- Offshore (southerly) winds were reported on 25 days (49%); these days accounted for 13% of days with at least one reported case of itch (2/15) but only 3 reported cases of itch overall. There were reports of itch on 8% of offshore wind days (2/25).
- There were 233 reported itch cases among 1509 estimated swimmers on days with onshore winds (15.4% incidence); 3 cases of itch were reported among the 2646 estimated swimmers on days with offshore winds (.01% incidence); 9 cases among 467 swimmers on days with an east wind (1.9% incidence); and 0 cases among 399 swimmers on days with a west wind. Overall incidence was 4.9% (245 reported cases among 5021 estimated swimmers).
- Although estimating the number of swimmers in the water is particularly problematic, it is interesting to note that the data show about 47% more swimmers in the water on days with offshore (southerly) winds than onshore (106 swimmers/day versus 72). This is not surprising given both the cold wind and waves of some north-wind days and the likelihood that awareness of the association of onshore winds and itch is changing swimming behavior.