After one of Madison’s longest, coldest winters ever, swimming season is almost here — along with toxic algal blooms, bacteria, invasive milfoil and other pestilences of the lakes. The Yahara lakes — Mendota, Monona, Wingra, Waubesa and Kegonsa — are no clearer than they were 30 years ago, despite intensive efforts to improve them. During that time, lake scientists said, the increased heavy rainfalls that are part of climate change most likely offset gains from better land use practices, by washing giant volumes of pollution into the lakes.