During the 1914-15 drought, saltwater penetrated even beyond Lake Alexandrina and up the river proper with a dolphin sighted at Murray Bridge and a shark at Tailem Bend.

In 1830, Charles Sturt, a fellow of the Royal Geographic Society and the explorer who gave both the Darling and Murray Rivers their names, described the waters of Lake Alexandrina as initially "sweet" but by the morning of the second day, as they headed across the lake he noted the waters suddenly became salty and "unpalatable" and that "the transition from fresh to salt water was almost immediate".

There is an argument, put to me recently by both Tim Flannery of the Wentworth Group of Concerned Scientists, and Greg Hunt, Shadow Minister for Climate Action, that if the barrages had not been in place during the recent drought, salt water would have penetrated an unnatural distance up the Murray River.

These opinion leaders seem to conveniently ignore that there was more water travelling down the river during this recent drought than in either 1914-15 or 1945-46, so there is no reason to suppose the intrusion would have been any worse than back then - before the completion of the Snowy Mountains scheme.

The bottom line is that the new guide is about taking water from our best food-producing farm land and sending it down to the Lower Lakes which were never a totally fresh water system and are now degraded by European carp and new housing developments.

Not so many years ago Bob Brown, leader of the Australian Greens, was claiming that it had been "scientifically proven" that 1.5 million megalitres were needed to solve the problems of the Murray Darling Basin.

Since then at least one milion megalitres have been bought back.

During the recent drought the river did not run dry, Adelaide did not run out of drinking water and the world's largest environmental flow release of 513,000 megalitres was made into the Barmah-Millewa forest.

And during this past year the basin has enjoyed flooding rains.

A reasonable person might conclude that we have finally got the balance right between irrigation and the environment, and along comes the new guide demanding even more water - ideally a whopping 15 Sydney Harbor equivalents be taken from irrigators.

The new plan makes a mockery of the word "science". Indeed there is no new science to justify the new demand for 7.6 million megalitres of more environmental flow.

Furthermore, most of the water will be sent down to the Lower Lakes, a region that did suffer during the recent drought, and unnecessarily, because the barrages could have been opened and the area flooded with seawater as happened naturally during previous drought.

Indeed, if the MDBA was serious about improving the natural environment of the most stressed part of the system, it would remove the barrages now blocking the natural ebb and flow between the Lower Lakes and the Southern Ocean.

* Dr Jennifer Marohasy is a biologist, research scientist, commentator on environmental issues and a firm believer that many of Australia’s major environmental debates are being driven by moral crusading rather than science.