 St Kilda 's marine environment of underwater caves , arches and chasms offers a challenging but superlative diving experience . Such is the power of the North Atlantic swell that the effects of the waves can be detected 70 metres ( 230 ft ) below sea level . In 2008 the National Trust for Scotland received the support of Scotland ’ s Minister for Environment , Michael Russell for their plan to ensure no rats come ashore from the <unk> , a UK @-@ registered / Spanish @-@ owned fishing vessel grounded on Hirta . There was concern that bird life on the island could be seriously affected . Fortunately , potential contaminants from the vessel including fuel , oils , bait and stores were successfully removed by Dutch salvage company <unk> before the bird breeding season in early April . 
