Relative frequencies of concentrations of total and faecal coliforms in cenotes of Cancun A frequencies of different concentrations of the Most Probable Number (MPN/100 ml) of total coliforms detected during dry (May-June) and rainy (September-October) seasons B frequencies of different concentrations of the most probable number (MPN/100 ml) of faecal coliforms detected during dry (May-June) and rainy (September-October) seasons. Frequency is plotted as a percentage of cenotes with the same concentration of MPN/100 ml. Bars with the same percentage but with both colours represents cenotes without changes between dry and rainy seasons.