A little-known tax on water that flows over Niagara Falls and other waterways is costing Ontario consumers more than $340 million a year in hydro fees, CTV News has learned.

Ontarians pay the government a tax to rent water that flows over certain areas to help fund other provincial services. The charge doesn’t appear on customers’ hydro bills, but the fee is costing billions.

In 2010, the charge added up to a total of $310 million per year. It has climbed steadily since then to $343 million in 2014, totalling more than $1.6 billion over the last five years.

“Nobody’s really been talking about it because nobody really understands it,” said Progressive Conservative energy critic John Yakabuski. “Nobody really knows about it. It’s kind of a secret tax.”

The water rental fee is not a product of the current provincial government. It was introduced by the Progressive Conservatives back when they were in power. The fee, however, has more than tripled under the Liberals and now adds more than $6 a month onto consumers’ hydro bills.

Critics say the water rental fee has left them wondering whether the government will begin taxing the wind that flows through turbines or the rays of sunshine hitting solar panels.

“I certainly don’t discount anything,” Yakabuski said. “We wouldn’t expect to see something like that happen except with this Liberal government.”

In its defence, the government says the revenue gained through the tax supports vital services that Ontarians rely on such as healthcare.

Neither Minister of Energy Bob Chiarelli nor the Minister of Finance Charles Sousa were available to comment on the issue, but both have previously stated that the province is doing everything it can to keep electricity prices down.

With a report from Queen’s Park Bureau Chief Paul Bliss