An apparent die-off of fish last week, thought to be caused by a toxic algal bloom or water contamination, turned out to be more mundane in its cause.

The many dead fish floating up on the Pembroke shoreline came from a castaway catch, according to a spokeswoman from the Ministry of the Environment.

North Shore residents contacted The Royal Gazette on Thursday to say that large numbers of small breams, yellow grunts, squirrel fish and others were coming in with the tide.

“This was investigated and found to be old frozen fish that someone discarded,” the spokeswoman responded.

Natural die-offs can occur at any point from late spring to late summer, and are tracked by the ministry.

The phenomenon is typically caused by blooms of algae, often in conjunction with coral spawning, that rob fish of oxygen.

Numerous dead fish around the reef platform were found in October of last year, prompting a warning not to consume any fish found in a weak state.