Provincial investigators have finished their review into the deaths of 500 ducks in a toxic oilsands tailings pond last spring.

The Canadian Press has learned that a decision will be made by mid-July on whether to lay charges against oilsands giant Syncrude Canada Ltd.

Alberta Environment spokesman Josh Stewart says a conviction for the charges being considered would carry a maximum penalty of $1 million.

Most of the ducks and other waterfowl that landed on the tailings pond at the end of April died within a few days, including the handful of birds that could be rescued.

Syncrude issued a public apology, explaining that noise-makers used to scare off birds had not yet been deployed because of a spring snowstorm.

The dead ducks were a major blow to Alberta's efforts to defend its environmental record against growing international criticism, including suggestions in the United States that the oilsands are a "dirty" source of energy.