“Correctly identifying an invasive species as either native or nonnative is important for developing sound policy, management and scientific research programs because effective responses depend on knowing whether the species' dominance is caused by ecological or evolutionary novelty, changes in environmental conditions that facilitate it, or both," Professor Brad Taylor, the study's lead author, said in a statement.

Rock snot blooms have been recorded as long as a century ago, yet “this information was either ignored or the idea of a new genetic strain was adopted,” Taylor said.

Algal blooms are often caused by excessive levels of phosphorous or other nutrients in freshwater, yet rock snot actually appears when the amount of phosphorous is low.

Here’s why: Didymo lives on the river bottom and draws its nutrients from the water above. When those nutrients are rare, the didymo produces long stalks that push higher into the water. The stalks then cause thick mats to cover the river bottom.

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