The dairy industry has had a good relationship with the marine farmers for the past five years after work carried out by the Aorere Catchment Group improved the number of days marine farmers could harvest.
But in the past few months the marine farmers have had three unexplained spikes that have dramatically reduced harvesting days and dairying has been blamed, along with the local council for not being tough enough on the dairy industry.
Spokesperson for the dairy farmers, Sue Brown, said they were "gutted and very confused" about the spikes in water quality that occurred outside of high-rainfall periods. So far, the dairy industry and the Tasman District Council (TDC) have not been able to identify the source of the problem, though the shellfish industry is adamant its testing process shows the high E.coli readings could be attributed to cattle.
"Part of the dilemma is whether we're dealing with a source or non-point source," she said. "It would be disappointing to find a point of source and it's a relief not to have found one, but it would be simpler for all parties if we could find a source."
Dairy farmers considered it a possibility the long period of "grey" weather through spring had caused run-off into the Aorere River, rather than an effluent mistake, she said, or high rainfall further up the catchment had flushed out sediment from earlier floods.
Whatever the reason, the multi million-dollar mussel industry in the bay beyond the river mouth has been disrupted because of high bacterial readings from its own testing methods and farmers have only been harvesting 50% of the time they could possibly harvest instead of the usual 75-80%.
Representatives from the dairy and marine farming industries have since met with Ministry for Primary Industries (MPI) and TDC to discuss the problem and find a way forward.
A working party has been established and Brown said there was a commitment for the two sectors to work together alongside the council and MPI.