Crowds enjoy a summer's day on Eastern beach in Corio Bay, Geelong. Photo: LUIS ENRIQUE 
If you are looking for a beach on the bay with the best chance of pristine waters, go west.
Eastern beach in Geelong and St Leonards beach on the Bellarine Peninsula appear to be the places to head to if you want the best chance of enjoying a swim in the cleanest possible water.
Of the 36 bayside beaches the Environmental Protection Authority monitors for water quality, the two spots in the bay's west have had the most consistently good forecasts.
Taking the plunge at Eastern Beach.
Taking the plunge at Eastern Beach. Photo: Luis Ascui.
For the past 26 days they have had an unbroken run of good forecasts.
The predicted water quality has generally been safe for swimming throughout the bay in the past month, although beaches along Melbourne's south-eastern fringe such as Mount Martha, Safety Beach and Rye have recorded 13 days of poor or fair conditions.
But it should be noted the data is based on forecasts rather than any daily water-quality readings.
Illustration: Matt Golding.
Illustration: Matt Golding.
The EPA beach reports use a mixture of weather forecasts, pollution reports and water data collected during the past 23 years to predict water quality at each beach on a given day.
EPA applied sciences group manager Anthony Boxshall said more than 500 water samples were collected last summer, with 97 per cent showing suitable swimming conditions.
Water quality at beaches often suffers in the days after heavy rainfall, such as on December 7 last year when every single bayside beach the EPA monitors was judged unsuitable for swimming.
Eastern beach – oddly enough the westernmost beach the EPA monitors – is one of Geelong's  most popular recreation spots and features an enclosed swimming area, diving boards and a children's pool.
Lifesaving Victoria operations manager Greg Scott said it was also one of two beaches that  lifeguards still monitored between flags rather than using jet skis to patrol the area.
He said the beach also had a reputation as a safe one and was popular with families with children, but he warned swimmers against complacency there, saying that as recently as Thursday, a child had become separated from their parent.
Mr Scott has his own theory on Eastern beach's water quality.
"Maybe it's because it is a long way from the Yarra," he joked.