A report in Carnagarve and the Foyle was done by Karin Dubsky, BA, MSc Coastal Ecologist on the environmental effects of situating the Sewage Treatment at Carnagarve. Here are extracts and summaries from it with recommendations.


Zostera marina is a marine flowering grass, which forms dense beds, with trailing leaves swimming in the water column. The grass can be up to 1m long. Beds can be very long-lived > 100 years.

To develop and maintain itself the plants in a bed require shelter, the right sandy or muddy sand stable substrate, clean transparent water, yet enough nutrients. So we find it in sheltered bays and lagoons from the lower shore to about 5 m occasionally down to 10m depth.

Provides Shelter and Food for Fish and Shellfish

Ecological significance: Seagrass stabilises the substratum as well as providing shelter, a substrate and foraging area for many organisms. Organisms may be grazing on the blades or sheltering in grass or roots. Or hidden in the micro habitats around the rhizomes, roots and in the sediment. Fish and shellfish feed and shelter in it.

Zostera marina beds, bed sizes and health have declined over the last 80 years across the world and in Europe. Sediment disturbance, siltation, erosion and turbidity resulting from coastal engineering and dredging activities have been implicated in the decline of seagrass beds world-wide.

In Ireland it is officially known to occur in 19 bays. However Coastwatch volunteers have found further beds in at least 3 bays including the beds in Lough Foyle.


In line with Biodiversity Convention goals governments are looking at ways to protect, manage and restore this species – important in its own right and because of the many ecosystem services it provides to other species including man.

Zostera marina is listed in the EU Habitats Directive as qualifying interest for Special Area of Conservation (SAC) site designation. Since 2004 the grass is also on the ‘List of Threatened and Declining Species and Habitats’ drawn up by the OSPAR Commission.

Designation: Almost all of the known sea grass beds in Ireland are located in protected sites. However official Z marina records did not include Lough Foyle as a bed location and the species rich outer estuary is not designated as Natura 2000 site under the Habitats or Birds Directive.

Local Divers

In 2012 a team of local divers and Coastwatchers with traditional knowledge of the area participated, initially coordinated by Karin Dubsky, later by the local Foyle Coastwatch group. Further records were gathered, during the autumn 2012 Coastwatch survey where blades of sea grass swept up and visible landward edges at spring low water were noted.

Summary of Results: A string of Seagrass Zostera marina patches and beds were found straddling the Lough Foyle Donegal coast from the Salt Pans (south of Carrickarory Pier) to north of Glenburnie Bay just short of Greencastle.

One of the 4 Donegal beds fringes Carnagarve beach and extends into the path of the proposed sewage discharge pipe. The landward boundary in waist deep water at low tide.

Plant health varied from excellent quality with lush, dense clean dark green exceptional long blades (some > 1.5m) in the seaward facing shelter of the old Moville pier, to healthy looking in the majority of the beds and patches.

Worst Hit

The worst hit areas were in the bed in the shallow bay north of Moville around Carnagarve beach. Bed quality improved again further north from Glenburnie. THe Carnagarve problem is thought to be recoverable though if sewage stopped flowing through it.

It was noted that before even reaching the beds and once the boat was above a bed that the seaward limit was full of small fish. Juvenile fish also flushed from grass beds when approached from shore side and molluscs, mainly winkles were grazing on the seagrass.

The Moville raw sewage outfall plume was seen to move along shore on an outgoing tide in the seagrass band line on one calm July day site research visit.

Missing at Moville Pier

Zostera grass was missing at Moville pier and just north, with first location of the next bed north in poor condition with part smothered plants, matching the descriptions of eutrophication impacts in the literature. It is urgent to tackle the known source of nutrient enrichment – raw sewage discharge at Moville pier and ensure that no other sources contribute.

The sewage pipeline at Carnagarve will run along the sea bed through the seagrass areas. The construction of the pipe would disturb it. Also, the seagrass is sensitive to heat and chemicals and the water pumped in would be heated and contain chemicals used to treat the sewage. Also, if there is a flood overflow raw sewage may be pumped in damaging it terminally.

Raw Sewage

If the Moville raw sewage outfall was removed it may be an area to prioritize for oyster bed restoration. Especially as native oyster stock is still found in the lough and the species is now red listed for protection and a species action plan has been drawn up in Northern Ireland.

In Lough Ryan UK, a planned sewage treatment plant discharge pipe was diverted from the lough to the open sea after risks of pollution impacts in case of malfunction were deemed too high.

Report Recommendations

The report recommends that this guidance be applied in all areas where seagrass can still be found in Ireland. That is in less than 100km of >7000 km of our shallow intertidal shoreline. That means urgent address of current raw sewage discharge problems and avoidance of bed damage from any construction works.

The discharge for the planned treatment plant should be relocated to ensure it is also suitable from a biodiversity point of view.

There are low sensitivity locations, away from valuable and threatened sea grass beds and prime restorable native oyster ground – Just like the planning decision in Lough Ryan