A busload of Year 11 students from Burnside High school is dropped off beside Harts Creek, near Leeston in Canterbury.
The fast-flowing waterway is surrounded by dairy farms. In the distance is Lake Ellesmere.
The students are here to learn about water quality and freshwater ecosystems with Waterwatch Trust educators Errol Wood and Kelvin Nicolle.
The Waterwatch Trust – which has been going for more than 20 years – operates an environmental outreach programme for school and community groups.
Last year about 2,200 students participated in one of its programmes.
Students undertake a range of hands-on tasks using scientific equipment to monitor the physical, chemical and biological parameters of waterways.
"We test things like nitrate levels, phosphate levels, the amount of oxygen, the PH, conductivity and also turbidity, which is the clarity of the water," says Errol Wood, as he sets out six student-learning kits on a grassy verge of the creek.
Kelvin and Errol are retired university lecturers who believe that the best way for today's teenagers to learn about the environment is to be in the environment.
"For us older people it's great to have young people hanging off our every word, which isn't common these days!" Errol says with a chuckle.
The outdoor programmes run by Waterwatch are free and it's not the first time Donna Lee, who is head of department for geography and tourism at Burnside High School, has booked in her students.
"The younger generation coming through are genuinely concerned about the future and I think this age group also realise that they're the ones inheriting [the problems] and they've got to try come up with some solutions. Because we cant keep on doing what we're doing and I think they are well aware of that."