An anonymous reader quotes a report from NPR: In 1858, sewage clogging London’s Thames River caused a “Great Stink.” A century later, parts of the famed waterway were declared biologically dead. But the latest report (PDF) on “The State of the Thames” is sounding a surprisingly optimistic note. The river today is “home to myriad wildlife as diverse as London itself,” Andrew Terry, the director of conservation and policy at the Zoological Society of London, writes in a forward to the report published Wednesday. Terry points to “reductions in pressures and improvements in key species and habitats.”

Among those species are two types of seals. Before the early 2000s, little was known about their whereabouts, but now “[both] the harbor seal and the grey seal can be seen in the Thames,” the report notes, from the river’s tidal limit west of London, through the center of the city and across its outer estuary. Another success story pointed to in the report is the avocet, a migratory wading bird which had become extinct as a breeding species in Britain by 1842 due to habitat loss. It began making a comeback after World War II, and over the last three decades has seen its population among the tidal Thames more than double, according to the report. The report highlights several promising trends. But it also cautions that work still needs to be done in other areas, and warns of the negative impact of climate change on the river, which is a major source of water for the city. Despite the improvements, the report notes that just last year a research paper found high levels of microplastics in samples of the Thames water column taken in 2017. “Experiments have shown that such microplastics can have detrimental effects on aquatic life, as well as turtles and birds,” reports NPR, citing National Geographic.