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Ten days ago a large spill, presumed to be from a stock truck, left a visible stain in a wide tarsealed lane beside State Highway 6 outside the Frankton Golf Course.
Mr Jarvis said ultimately, cleaning the mess was up to the person who was responsible for the spill, but because such people were hard to identify, the agency was often left to clean the state highways.
After seeing a photo of the Frankton incident, Mr Jarvis said: ''That's quite an extreme case''.
''It's not easy at all to clean up,'' he said, because pouring water over it then using a ''road broom'' can make ''a bad situation worse''.
He said effluent spills were becoming more frequent in Central Otago, as more land was irrigated for grazing.
A multi-agency approach was being taken to make farmers more aware of their responsibilities.
While two more effluent storage tanks are proposed in the Otago Regional Council's draft annual plan, the answer was ultimately a ''combination of standing [off green feed overnight] the stock and taking personal responsibility''.
Road Transport Forum New Zealand chief executive Ken Shirley said cattle beasts could produce 10 litres of effluent each an hour, meaning trucks could be laden with nearly half a tonne of effluent when carrying 45 cattle.
Trucks had a mechanism to release effluent holding tanks, but this was not in the cab.
Much dairy stock is transported from Southland to Otago at the moment.
Mr Shirley said spills ''shouldn't happen [because] there are meant to be adequate dump sites'' and farmers had the responsibility to stand their stock, although ''often that doesn't always happen''.
The Otago Regional Council has seven storage tank sites.
It would cost the NZTA ''a few hundred [dollars]'' to have a contractor clean Tuesday's spill, Mr Jarvis said.
''It's placed in a terrible spot, right in an urban area. It appears as though the truck was stationary.''
He said he would ''like to think no-one would deliberately dump that load right [there]''.
Spills in rural areas were usually left to disintegrate unless they could become slippery and frosty.
''It's an annoying thing for everyone,'' Mr Jarvis said.