Complex sentence: The regatta was inaugurated in 1877 with events for sweep-oar pairs, sculls (as racing shells), punts, canoes and swimming--for the first fifty years Sunbury hosted a parallel Tradesmen's or Town regatta for professional watermen.
Split into simpler sentences: The regatta was inaugurated in 1877 with events for pairs, sculls, punts, canoes and swimming. For the first fifty years there was a parallel Tradesmen's or Town regatta for professional watermen.