Booterstown Marsh Nature Reserve is located in Booterstown, County Dublin between the coastal railway line and the Rock Road. It is a salt marsh with brackish water, covering an area of approximately 4.3 ha. It was fed with freshwater from Trimleston stream, and has a tidal inflow under the railway track which runs directly along the edge of Dublin Bay, forming a sea wall at Booterstown.
An Taisce administer the marsh having acquired a lease to it in 1970, and have designated it a Bird Sanctuary.
Originally, the area occupied by Booterstown Marsh was part of Merrion Strand and was part of a fringe marsh from Dublin city to Blackrock. Over time, much of this marshland was lost due to reclamation.
The current marsh resulted from the building of the Dublin and Kingstown (now Dún Laoghaire) railway line, which was one of the first in the world, from 1834-35. The line was built on an embankment, protected by a granite seawall. In the 1830s, the resulting tidal lagoon covered more than 28 ha. In the following decades much of the area was filled in, leaving only Booterstown marsh still subject to flooding by seawater at high tide.
By 1876 this reclaimed land was in agricultural use, made possible by the use of water control systems. A large gate valve was installed at the Williamstown (southern) outlet to the sea, which was lowered on the flow tide and raised on the ebb tide. The Williamstown lagoon acted as a sump, collecting the water draining from the agricultural land. Some landfill soil raised the level of the marsh and it was irrigated with fresh water from a number of local streams.
During both World Wars the marsh was used as allotments, however with increasing prosperity these fell idle and in the 1950s the area was used as pasture. The water control systems were also neglected, allowing salt water to enter the system.
By the 1970s the marsh showed salty vegetation at the railway side and fresh-water at the inner edges. This mixed habitat became an important site for many marsh bird and plant species. In 1970 the lease on the land was acquired by An Taisce, a conservation society, which has managed it as a nature reserve.
Oil spills in 1982 and, more severely in 1985, led to de-oxygenation of the marsh. The vegetation was dominated by Scirpus maretimus, a rush that could withstand the conditions, though the re-discovery of a rare species of grass following some works on the drainage enhanced the conservation status of the marsh.
In response the flap valves were removed, allowing a free flow of salt water that is rich in oxygen.
At present the condition of the mud has improved, and birds have returned in large numbers. The Scirpus growth has significantly reduced, and of the many species of plant occurring in the marsh, one of them, Puccinellia fasciculata which is protected, along with its habitat. There are three main habitats ranging from freshwater to saltwater and the area attracts Moorhen, Reed Bunting, Sedge Warbler, Common Teal, Common Snipe, Northern Lapwing, Eurasian Oystercatcher, Common Redshank, Little Egret, Dunlin and Brent Goose.