Lake Sommen
... that one theory holds that aquatic cold-water species entered Sweden's Lake Sommen by a natural lock system at the end of the last ice age?
... that one theory holds that aquatic cold-water species entered Sweden's <b id="mwBQc"><a href="./Sommen" id="mwBQg" rel="mw:WikiLink" title="Sommen">Lake Sommen</a></b> by a natural <a href="./Lock_(water_navigation)" id="mwBQk" rel="mw:WikiLink" title="Lock (water navigation)">lock system</a> at the end of the <a href="./Weichselian_glaciation" id="mwBQo" rel="mw:WikiLink" title="Weichselian glaciation">last ice age</a>?