J. Deely et al., ENTEROCOCCAL NUMBERS MEASURED IN WATERS OF MARINE, LAKE, AND RIVER SWIMMING SITES OF THE BAY-OF-PLENTY, NEW-ZEALAND, New Zealand Journal of Marine and Freshwater Research, 31(1), 1997, pp. 89-101
In the Bay of Plenty, New Zealand, 32 coastal beach sites, 23 lake bea
ch sites, and 31 river swimming hole sites were sampled for enterococc
i as indicators of bathing suitability over 3 summers (from 1991 to 19
95). The median enterococcal numbers of 5 samples collected from each
site over each season were compared to the guideline medians: 35 and 3
3 enterococci per 100 ml for marine and fresh waters, respectively. Th
e ''5-sample median'' values generally agreed with longer-term medians
(n = 24, 28) from river and estuary sites sampled between 1990 and 19
94. During the summers of 1991 and 1993, high enterococcal numbers at
marine and lake swimming sites were assumed to be derived primarily fr
om sewage effluent and farm run-off, either directly or from freshwate
r inflows. Enterococcal numbers dropped significantly in these waters
when effluents were either treated or removed from the waters. In 1995
, all marine bathing waters complied with the guideline value of 35 en
terococci per 100 mi. Evidence from long-term monitoring of estuary si
tes indicated that most marine bathing sites have high-quality bathing
water with short-term variability caused by winds, tides, and outfall
discharges. In 1995, all but one lake site complied with the freshwat
er median guideline of 33 enterococci per 100 mi. Most upstream river
sites also complied with the freshwater guideline. However, river site
s in the mid reaches and down stream recorded high enterococcal number
s which increased slightly at some sites from 1992 to 1995. The most s
ignificant increase in bacterial numbers was recorded in the small riv
er and stream swimming holes which carry low volumes of water (< 1000
l s(-1)), particularly in the western area of Lake Rotorua. The main s
ource of enterococci in river waters was most likely run-off from dair
y farms on the flood plains of the various rivers of the Bay of Plenty
.