Water Research 38 (2004) 79–88 Statistical analysis of the fluctuating counts of fecal bacteria in the water of Lake Kinneret Ora Hadas a , Maria G. Corradini b , Micha Peleg b, * a Israel Oceanographic and Limnological Research, Yigal Allon Kinneret Limnological Laboratory, P.O. Box 345, Migdal 14950, Israel b Department of Food Science, Chenoweth Laboratory, University of Massachusetts, Amherst, MA 01003, USA Received 12 March 2003; received in revised form 5 August 2003; accepted 3 September 2003 Abstract Counts of E. coli, Enteroccoci and fecal coliforms in four sites around Lake Kinneret (The Sea of Galilee), collected every2–4weeksforabout5yearsduring1995–2002showedirregularfluctuationspunctuatedbyaperiodicoutburstsof variable magnitude. Because of the haphazard nature of fecal contamination and large intervals between successive counts, these patterns were described by probabilistic models, based on the truncated Laplace or Extreme Value distribution. Their applicability was tested by comparing the predicted frequencies of counts exceeding different levels calculated from the first half of each record with those actually observed in its second half. Despite the records imperfections and minor violations of the underlying models’ assumptions, there was a reasonable agreement between the estimated and actual frequencies. This demonstrated that it is possible to translate the irregular fluctuation pattern into a set of probabilities of future high counts. In principle, such probabilities can be used to quantify the water’s fecal contamination pattern and as a tool to assess the efficacy of preventive measures to reduce it. r 2003 Elsevier Ltd. All rights reserved. Keywords: Coliforms; Enterococci,Water contamination; Jordan River; Mathematical models; Predictive microbiology; Sea of Galilee 1. Introduction Fecal contamination of water sources has always been a major safety concern and a factor in determining the need of a treatment. The Lake Kinneret watershed and Jordan Valley are important parts of the Kingdom of Jordan and the State of Israel. The peace treaty between the two countries includes a water sharing agreement and hence the water quality has a political as well as public health dimension. Consequently, quantitative assessment of the microbial quality of the water in this region has become particularly important and urgent. A major difficulty in assessing the microbial quality of water in streams and reservoirs, apart from the questions of sampling and culturing the organisms of interest, is the irregular nature of their abundances. They usually fluctuate widely and are punctuated by aperiodic outbursts of unpredictable magnitude and duration. Oscillating populations have been tradition- ally described by models based on population dynamics [1–3] and chaos theories [4–5]. However, their success in accounting for microbial presence in natural habitats hasbeenlimitedbecausetheintervalsbetweensuccessive counts is usually too long to follow the population’s evolution in sufficient details. Also, the microbial population’s response to local environmental changes and its relation to accidental contamination cannot be revealed by periodic counts if these are too widely spaced. This is particularly true for fecal organisms, which can reach a water reservoir in totally unpredict- able ways. Nevertheless, in many places, because of logistic considerations, this is the only feasible option to monitor the water quality and the result is records of very limited value for formulating a population ARTICLE IN PRESS *Corresponding author: Tel.: +1-413-545-5852; fax: +1- 413-545-1262. E-mail address: micha.peleg@foodsci.umass.edu (M. Peleg). 0043-1354/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2003.09.004