But last summer's biblically proportioned haul of fish was not the kind of experience any of the lake's visitors had in mind.

Tens of thousands of dead fish washed up on the lake's grassy beaches one January weekend – mostly loathed European carp but also redfin, native Murray cod and yellowbelly.

It forced a huge community clean-up in the intense mid-summer heat and the stench of rotting fish put paid to holiday activities for several days, locals say.

Now they want to know if the mass fish kill was just an act of nature as authorities have claimed, or a result of mismanagement of water in the Murray-Darling basin.

The fish in Lake Meran were killed by what's known as "black water".

This happens when flood waters rise in a river system that has long been dry, and pick up masses of leaf litter that starves the water of oxygen.

There have been several black water events in northern Victoria in recent years, as floods followed the end of the Millennium drought.

Some have killed large numbers of native fish and river crays.

This week, a state parliamentary inquiry will begin in an effort to learn more about why Victoria's northern rivers and lakes have suffered a series of black water events since 2010, and whether the practice of strategically releasing water into the Murray-Darling for the environment is to blame.

The inquiry will tour towns close to where black water events have hit, including Kerang, Shepparton and Wodonga.

Kerang resident Ron Kelly witnessed the huge fish kill that hit Lake Meran on January 8 and 9.    

Part of a group called Friends of Lake Meran, he said locals who use the lake were still searching for an answer about the cause of January's devastating event.

"The EPA said it was due to a build-up of carbon in the water from the flood that had come through, but there is debate from some people in the area," Mr Kelly said.

The debate concerns whether the black water was caused by the natural flow of floodwater from the Loddon River, or if it was from decaying knotweed that had grown on the lake bed, exposed after authorities kept the lake below its maximum level.   

"We can't really know because I don't think there has been a proper study done as to whether it was one or the other or a combination of both," Mr Kelly said.

The inquiry was initiated by Victoria's Nationals.

Stephanie Ryan, the Nationals' water spokeswoman, said there was "significant concern in northern Victoria about the potential for environmental watering to create black water events".

"They have a huge environmental, economic and social impact on those communities on the Murray that are heavily dependent on irrigated agriculture and tourism," Ms Ryan said.

But the inquiry will also hear evidence that black water events are simply part of nature and that environmental flows are blameless.

The Murray Darling Basin Authority, which is in charge of balancing thousands of gigalitres of water a year for agriculture and the environment, said mass fish kills had been recorded in newspaper reports since the 1860s.

"Black water events are alarming and distressing, especially when the deaths of large numbers of native fish occur," the authority said.   

"However, low oxygen events have long been a part of the fabric of our river history."

The Andrews government also argued black water was simply a natural phenomenon that followed heavy rains.

Water Minister Lisa Neville said the Murray-Darling needed environmental water "to protect plants, fish and the overall health of rivers, wetlands, floodplains and waterways".

She said changes in the management of flows into Lake Meran would not have prevented last summer's large-scale fish kill.

- The Age