An up-close look at the bad bugs hiding in our lakes, according to scientists

An up-close look at the DNA hidden in our lakes confirms the effects of on-land activities on our waterways, according to scientists.

A team of researchers from Lincoln University, Cawthron Institute, Earth Sciences New Zealand and James Cook University took samples of environmental DNA, or eDNA as they call it, from 287 lakes, from those in an almost-pristine state, to those more obviously polluted.

They found 412 separate pathogens - some just in the water and some found both in the water and the sediment underneath.

"In New Zealand, we have about 5200 lakes and of those around about 45 percent are what we would say are in poor or worse condition, so they've got high levels of nutrients, and often in summer they'll have algal bloom," study co-author and Lincoln University Professor Susie Wood said.

"Those lakes that are in poor condition tend to be places where there's human activities around them, so whether that's horticulture, agricultural, urbanization, so everything we do on the land has, of course, has a big impact on our on our freshwater systems."

The human influence on the health of lakes had only happened within the past 70 years, according to the researchers.

The study shows just how useful eDNA can be as an early detection screening tool, Wood said, and how used alongside other testing methods, it had the potential to improve monitoring of lakes.

"It's a fantastic tool for things like biosecurity, so when a non-native species arrives in a lake, you want to detect it early, and hopefully take actions to to prevent it from from spreading."

Citizen scientists were benefiting from the technology too, with a community group even using eDNA to detect previously-undiscovered mussels in its catchment area, prompting it to do something to protect the land around the stream.

"As researchers, the sort of work that we're doing is making sure that we know how to sample our systems effectively, so we know how many samples we have to take from our lake to detect the fish or the species of interest and what methods we should use."

Wood said eDNA wasn't a replacement for other testing methods but did allow researchers to do things at higher resolution or greater scale.