The speculation of bull sharks possibly being responsible is based on some attacks occurring in brackish and freshwater.
en.wikipedia.org The complex array of freshwater and brackish lakes, riparian areas, and wet meadows, provide habitat and large, undisturbed, tracts for a variety of wildlife species.
en.wikipedia.org It prefers mangroves and rarely leaves this habitat where it favors open shallow ponds and lakes, preferably brackish.
en.wikipedia.org They inhabit inshore coastal areas such as coastal lagoons, estuarine environments, and the lower, brackish river deltas.
en.wikipedia.org Historically, the interaction of the rivers flow and the oceans tide created a dynamic environment, supporting freshwater, brackish, and saltwater species.
en.wikipedia.org