Tanya Plibersek, who will embark on a tour of the southern basin on Wednesday and Thursday, conceded delivering on the plan's mid-2024 timeline would be "very challenging indeed", a view that has been reiterated in several parliamentary reports and inquiries.

"There are some very big challenges, a lot of this stuff has been left to the last minute," Ms Plibersek said.

"I was surprised to come into a new portfolio... these long-term targets have been known for some time but have simply been allowed to drift.

"I don't understand why the previous federal government has allowed the plan to drift in this way. It is extremely disappointing."

Should the deadline not be met, Commonwealth legislation requires the federal government to recover any water shortfall. During the election, Labor said compulsory water licence acquisitions were not part of the party's policy, but did not rule it out.

"It's very early to be asking about buybacks - it's not in our plan, but I'm not about to close off options at this early stage," Ms Plibersek said.

Although delivering the plan in full - including the 450GL of environmental water - was a key election promise, Ms Plibersek deferred answering questions about how to get the plan back on track until she had toured the whole basin.

"One reason for this trip is to find some answers to these questions," Ms Plibersek said.

"I cannot give you answers before I speak to stakeholders, that would be highly improper in my view and unfair to stakeholders, I have to listen to those most affected by this.

"It's a big problem and I'm not pretending for a minute that this isn't a difficult task."

A missing piece of the puzzle is NSW's Water Sharing Plans, which are three years overdue. A handful were submitted to the Murray-Darling Basin Authority for approval at the end of June and the remaining are expected soon.

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Inspector-General of Water Compliance Troy Grant recently warned if NSW's plans were delayed further, or submitted and rejected, he would request Ms Plibersek to get the Commonwealth to intervene and create the plans for NSW.

Ms Plibersek kept her cards close to her chest when asked about Mr Grant's request.

"I've spoken directly with the NSW Water Minister and the Inspector-General, and I'll keep those conversations confidential for now," she said.

"We're trying to sort this out in a cooperative and collaborative fashion. Hopefully we are coming to a conclusion [with NSW's WSP].

"I am not sure why the previous government didn't work more closely with the NSW government a bit earlier."

Ms Plibersek will meet with several stakeholders across her two-day tour of the southern basin and promised to a northern basin tour would follow.