Environment Protection Authority samples showed poor water quality across many beaches, with bacteria levels higher than the 400 organisms per 100ml of water benchmark deemed safe for swimming.

EPA spokeswoman Tanya O’Shea said last week’s rainfall caused the spike.

“This is due to run-off from rainfall and stormwater, which deposits litter, debris and even dog droppings onto the local beach,” she said.

The EPA tests measured enterococci, or e.coli, which is the bacteria found in faecal matter from animals and humans.

E.coli levels above the 400 organism mark showed up throughout the bay last week, including readings of 510 at both Mordialloc and Beaumaris. Mordialloc recorded levels of just 10 the previous week and 10 in the same week last year. Beaumaris recorded 160 the previous week and less than 10 in the same week last year.

Hampton levels jumped from 20 organisms on January 2 to 460 last week.

Bacteria levels were better in Brighton, with less than 10 organisms recorded during mid-week testing.

The EPA has four water quality ratings: good, fair, poor and unacceptable.

The EPA advises against swimming when water is rated ‘‘poor’’. When water is rated ‘‘fair’’, it is deemed acceptable for swimming.

Beaches around Bayside and Kingston ranged from fair to poor last week.

Ms O’Shea advised people not to swim near stormwater drains and rivers for 24 to 48 hours after rain.

The EPA provides summaries on its website, at epa.vic.gov.au/beachreport