On Thursday Miss Bocker, an MSc graduate, had 12 sites in the Whanganui and Rangitikei districts to check. She started at William Birch Pool near Maxwell and finished at Lake William, near Bulls.
She travels in a car loaded with equipment. The first stop with the Wanganui Chronicle was Mosquito Point, where she usually finds some swimmers. She put on waders and a life jacket and took photographs of the river first.
Then she waded as close to the main current as possible and filled two small bottles with water from below the surface - water at the surface can have extra bacteria. They were labelled, noted on a chart and kept cool in a chilly bin to prevent bacteria multiplying.
As well as repeating this at each site, Miss Bocker talks about the programme to anyone who asks, and also spreads the word about checking, cleaning and drying footwear and equipment between waterways - to prevent the spread of the invasive algae didymo.
On rivers with rocky bottoms, she'll use a periscope to see how much freshwater algae is coating the rocks. Every month at each site, and weekly at lakes, she takes a one litre sample to check whether algae are at bloom levels.
In this windy season she's had waves splashing her and sand blown in her face at beaches, and sometimes worked in near-horizontal rain.
In the Whanganui and Rangitikie districts swimming is good in the sea, she said, unless recent heavy rain has discoloured the water. Lakes can have problems with algal blooms. There is a health warning over a bloom at Dudding Lake at present.
Rivers and streams are variable. At the moment Mowhanau Stream is subject to health warnings, because of sewage leaks from a Whanganui District Council system. It often has the "red light" on the Horizons map - warning swimming could be hazardous.
Another place often labelled "no go" for swimming is William Birch Pool. It and Mowhanau Stream are being investigated by Horizons.
The Whanganui and Rangitikei rivers are generally good for swimming, unless they have been discoloured by recent rain. Oddly, Mosquito Point can have worse results than the river at the City Marina.
With her scientific mind, Miss Bocker isn't jumping to any conclusions about the reasons for water quality. She said those things have to be discovered.
"Where we are getting results we aren't happy with, we can pass those on to teams to look at more closely. We're providing clues, about which areas to look at."