Avista shares tumbled after Washington state regulators denied approval of its acquisition by a Canadian utility.

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Shares of Spokane-based Avista fell 13 percent  Thursday after the Washington Utilities and Transportation Commission said its proposed acquisition by Canada’s Hydro One doesn’t adequately protect Avista or the utility’s customers from political or financial risk.

Avista shares  closed down $6.71 to $44.68, their lowest level since the companies announced the $5.3 billion deal in July 2017.

“The companies are extremely disappointed in the UTC’s decision, are reviewing the order in detail and will determine the appropriate next steps,” Avista said in a statement following the commission’s denial of the sale.