Invasive weed finally meets its match

A SPECIALLY designed weed-cutting machine, which has been introduced to Lough Corrib to tackle an invasive plant, may yet be seen in other parts of the country.

The Italian-built OSMA machine meets many of the specifications needed to curb the highly invasive, curly-leaved waterweed (lagarosiphon major).

Its introduction to the western lake is a key step forward in the battle to control, and, if possible, eradicate the weed.

Lough Lein, the biggest of Killarney’s lakes and centrepiece of the area’s tourist attractions, also has invasive weeds in abundance, as can be seen by anyone taking a walk on the shoreline at Ross Castle. In a few years, underwater weeds have taken hold and grown rapidly, to the annoyance of anglers and boatmen.

Our rivers and lakes, already damaged by pollution, could fall into an even more serious condition because of government financial cutbacks, however.

Concern is being voiced that little is being done to halt the spread of invasive species, now regarded as being second only to habitat destruction in the league table of main dangers to our environment.

Curly-leaved waterweed, which originated in South Africa, is an underwater plant that was introduced to Ireland for use in garden ponds and aquaria, but has been spreading rapidly since 2005. It can restrict the movement of fish, boats and cruisers and is proving to be detrimental to tourism angling, as well as expensive to deal with.

The Central Fisheries Board, and other State agencies, are jointly involved in the OSMA project, which could set a headline for other infected areas. While fishery boards and other bodies acknowledge research is also being carried out to combat the threat, they claim the Government is failing to act to protect our waterways.

The South Western Regional Fisheries Board says that to protect areas such as the Killarney Lakes, a special programme needs to be devised. It is also calling for limited access to the lakes and mandatory boat-cleaning protocols. Board manager, Aidan Barry, said once the weed becomes established it can significantly alter the ecology of an infested watercourse. As it grows rapidly, it easily displaces aquatic plants and insects. “The board suggests that, in order to protect such valuable areas as the Killarney Lakes, a bio-security programme be drawn up,” he said.

Two invasive plant species have been recorded, and have increased at a worrying level, at a beauty spot in Lough Lein, according to a report, leading to fears for tourist leisure boating and angling, as well as fish stocks.

Canadian pondweed (Elodea canadensis) is now found in Ross Bay, alongside Ross Castle, a popular angling and boating lake visited by thousands of tourists.

The weed’s more aggressive cousin, Nutall’s Pondweed (Elodea nuttallii), has also been found in the bay and is increasing rapidly, according to Kerry County Council’s environment section.

Killarney councillor, Michael Gleeson, warned boating would soon be impossible, as engines were being clogged up by the weed, which was first documented in the area three years ago.

Originally a native of north and south America, Canadian Pondweed was probably introduced here through imported aquatic garden plants. Cutting in early spring can prevent its spread.

Nuttall’s is more virulent and less easy to control, according to South Western Regional Board and Central Fisheries Boards, which are carrying out a study into its occurrence at the Carrigadrohid reservoir, in Co Cork.

Both weeds choke oxygen and light from the water, and can grow submerged in the water for several metres. One of the reasons the invaders are flourishing in Killarney, it is believed, is because of nutrient enrichment of the lake, which has been polluted since the 1970s.

Curly-leaved waterweed is regarded as a nuisance in its native South Africa. The plant can grow in water up to six metres deep. In addition to occupying the full water column, plant stands produce dense vegetation on the water surface.

Detached stems, when they sink, root from the nodes and establish new populations.

According to the Central Fisheries Board, the weed can cause fish kills through oxygen depletion and is potentially a bigger threat than the Zebra mussel.

It can also be spread by fragmentation via wind dispersal, boat movement, angling equipment, and, possibly, waterfowl. The weed will grow in lakes, rivers, streams, canals and ponds.

An expert group with international experience in aquatic weed management has been convened to determine and implement all possible options for the control and elimination of curly-leaved waterweed.

Lake users are urged to always thoroughly clean boats, trailers, engines, angling equipment and waders when leaving the waterway.

Lake users are also asked not to introduce any weed to any watercourse, not to dispose of invasive plant material in the vicinity of any watercourse, and not to drive boats through established stands.