Field studies were carried out to evaluate the potential impact of removal of Rustico Island Little Harbour Causeway, Prince Edward Island on water quality within Rustico Bay. This study was part of a larger project to evaluate various remediation scenarios proposed to improve both water quality within the Bay and navigability within the entrance to North Rustico Harbour. The project was carried out jointly between the Acadia Centre for Estuarine Research, the Geological Survey of Canada (Atlantic), Baird and Associates Ltd. and Challenger Oceanography. The major objectives of the water quality component of the project were to determine existing water quality within the Bay and the two rivers entering the Bay, and to determine how water quality would be affected by each of the proposed remediation alternatives.

A total of four water quality transects were carried out, one on the Hunter River system and three on the Wheatley River system. Parameters measured included salinity/temperature depth profiles, Secchi Disk depths, and concentrations of chlorophyll a, dissolved oxygen, suspended sediments, and nutrients. In addition, studies were carried out to determine the organic and nutrient concentration of sediments at 15 sites within the Bay in order to evaluate the potential water quality impact of sediment organic and nutrient resuspension that may occur as a result of the proposed remediation options.

The water quality survey indicated only the area of the Wheatley River above the highway bridge to be seriously degraded, particularly with respect to dissolved oxygen levels. The lower Wheatley estuary and the entire Hunter River system, although characterised by relatively high nutrient inputs, did not exhibit any evidence of low dissolved oxygen concentrations or excessively high algal concentrations. The relationships observed between nutrient concentration and salinity indicated that nutrient inputs to these areas are diluted by seawater. This, together with the high oxygen concentrations present in seawater and the lack of any significant water column stratification within the Bay, keeps Rustico Bay from becoming oxygen depleted.

There was little indication that any of the proposed remediation alternatives would have a significant impact on the degree of tidal flushing that presently exists within Rustico Bay and, as a result, little improvement in water quality is to be expected from their implementation. In addition, none of the proposed remediation options is predicted to result in significant resuspension of existing sediment nutrients and organics and it is unlikely that this would be a major concern in terms of impacting water quality.