Bill Nelson and Rick Scott on Friday sharply escalated the political fight over the Lake Okeechobee toxic algae crisis.

Scott's campaign launched a TV ad accusing the Democratic senator of having failed to act, and Nelson blamed the Republican governor for a war on environmental regulations.

Nelson said the problem is with the state. Scott said it's the federal government's fault.

"Washington politician Bill Nelson made a pledge thirty years ago to solve this problem," goes Scott's ad. "But Nelson is a talker, not a doer. With Bill Nelson, we get more waiting, more talk, and more algae."

The ad invoked a campaign pledge Nelson made in 1990 to "save Lake Okeechobee and make polluters pay for the cleanup." (Nelson ran for governor that year, though Scott's ad omits that point.) Nelson's campaign did not respond to that charge and largely cited more recent steps to address Lake Okeechobee and water issues.

Nelson's office issued an "open letter" to constituents Friday noting that over the past 20 years, the U.S. Army Corps of Engineers has spent more than $1 billion to strengthen the dike to prevent a "massive, catastrophic breach that could kill thousands of people living south of Lake Okeechobee – and we have just authorized an additional $600 million to speed up the completion of the dike by 2022."

[Read more: Florida's politicians use slimy algae to muddy each other]

Nelson then turned things on the state (and implicitly, the two-term Scott) for having "repeatedly rolled back environmental standards, eased regulations and dismantled the state's environmental agencies."

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Nelson could find ammunition in one of Scott's first actions after first winning election in 2010, when he joined a letter protesting "onerous regulation" from the Environmental Protection Agency under President Barack Obama.

Read the letter in its entirety (portions were highlighted by Rick Scott's U.S. Senate campaign).

Nelson on Friday was visiting Stuart for a round-table discussion on the algae crisis.

Some Scott opponents have pointed to the significant financial support he's gotten from the sugar industry, which has been blamed for water pollution. But Nelson, too, has taken sugar money, if at lower amounts.