Complex sentence: The Aegir occurs when a high spring tide meets the downstream flow of the river, the funnel shape of the river mouth exaggerates this effect, causing a large wave to travel upstream as far as Gainsborough, Lincolnshire, and sometimes beyond.
Split into simpler sentences: The aegir occurs when a high spring tide meets the downstream flow of the river. The funnel shape of the river mouth exaggerates this effect, causing a large wave to travel upstream as far as Gainsborough, Lincolnshire, and sometimes beyond.