The health of many rivers and streams throughout San Diego County — which flow down canyons and wind through often contaminated urban landscapes — has improved after suffering during several years of drought conditions, according to a report released this week by the nonprofit environmental group San Diego Coastkeeper. While pollution continues to significantly impact all watersheds in the region, Coastkeeper’s annual water-quality monitoring report found markedly cleaner waters in 2016 compared to the previous two years. That includes monitoring done in the San Diego, Sweetwater and Otay watersheds.