Thanks to laws such as the Clean Water Act, and the Safe Drinking Water Act, tremendous progress has occurred in the past forty years: the Cuyahoga River no longer catches fire, Boston Harbor is generally free of fecal matter, and municipal water supplies are generally much safer. As previously noted on this blog, however, water pollution has been and remains a major vector for public health hazards. Especially in light of climate change, low-lying, downstream and coastal areas are subject to increasing environmental health and justice concerns as polluted lower-order streams add in to major waterways. Increased flood risks add to the anticipated disease burden of these areas. One of the most visible results of this systematic inadequacy is the number of water bodies experiencing massive phytoplankton blooms and subsequent “Dead Zones.”
NASA map of Dead Zones around the world
As the above graphic shows, virtually all coastal waters surrounding industrialized nations are hypoxic. According to a 2008 study, “dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers.” For example, as previously noted on this blog, 66% of the near-shore water in Lake Erie is nutrient-impaired. The extent of Lake Champlain’s growing cyanobacteria problem has worsened so much that it was recently been the subject of a documentary. Similarly, the Chesapeake Bay Dead Zone in Maryland’s waters has averaged 22.1% of the volume in the Bay over the past 26 years (1985-2011). Likewise, the average size of the Gulf of Mexico Dead Zone surrounding the Mississippi River Delta has more than doubled since the 1980s.
Generally speaking, greater amounts of rainfall correspond with larger blooms, as the runoff washes more nitrogen and phosphorus into watershed systems. Beyond extreme weather increasing nutrient loading of surface waters, the simple fact of the matter is that warmer global temperatures are more conducive to bloom formation. Thus, while blooms are harmful in their own right, they also serve as an indicator of climate change. As the likelihood of extreme weather increases due to climate change, it seems logical to assume that there will be corresponding shifts in the extent of algal blooms and aquatic dead zones. 
For example, following Hurricane Irene in 2010, the summer of 2011 produced a record-large dead zone in the Chesapeake Bay and the greatest range of blooms in Lake Champlain’s history. Conversely, the relative drought preceding the summer of 2012 resulted in the smallest dead zone in the Bay since 1985. Similarly, the summer of 2012 also saw the fourth-smallest dead zone in the Gulf of Mexico since 1985. The full effects of Superstorm Sandy on watershed (and therefore public) health will presumably show themselves more fully in the summer of 2013.
The above schematic shows that lobal climate disruptions are likely to have profound impacts on public health. As mentioned, the extent of blooms and subsequent dead zones are both indicators of the climate change problem and contributory threats to food and water supplies. The most serious impacts of all of this will necessarily fall on the poorer segments of society, e.g., those communities most likely to lack the resources to implement necessary improvements to compensate for these impacts. Again, as previously discussed, some cyanobacteria blooms produce toxins with a variety of deleterious effects. Other planktonic species pose similar health threats.
More worryingly, there is “good evidence that V. cholerae [cholera] survives in marine waters in a viable but non-cultural form that seems to be associated with algae and plankton,” meaning that blooms are potential indicators of a coming cholera outbreak. Specifically, phytoplankton blooms serve as a food source for zooplankton, with which cholera bacteria are associated. Thus, when the temperature rises “by 1 degree Celsius, there is a chance of cholera cases doubling in four months’ time.” Likewise, a 200-millimeter increase in the monthly rainfall total also corresponds with an increase in cholera within two months. This statistic is particularly alarming, since blooms can cause the water temperature in the bloom zone to rise to 1.5°C above those of ambient waters. If this were not already depressing enough, drought events and subsequent saltwater intrusion are also linked to cholera outbreaks.
As another example of the health hazards posed by climate change, a 2001 study concluded that 51% of all outbreaks of waterborne disease in the U.S. between 1948 and 1994 were preceded by an extreme rainfall event. At least one reported outbreak of cryptosporidiosis has been linked to rainwater flows across cattle pastures, after fecal-contaminated waters entered groundwater drinking supplies through a borehole. Concerningly, a study of Lancaster County, PA land use found that over 21% of the cattle farms were located within 100-year floodplain boundaries, and that on 64% of the farms at least one sample was positive for C. parvum, and 44% of the farms had oocysts in all manure samples.
It is true that developed countries are relatively insulated from post-flooding disease outbreaks. However, there is a direct correlation between the increase in severity of flood events and the probability that treatment works will themselves be flooded or otherwise overwhelmed. The likelihood of flooding and associated diseases increases even more once we factor in rising sea levels. 
The aftermath effects of floods also include compromised hazardous material impoundments, mold growth in houses, and increased populations of/exposure to disease-carrying pests. New Orleans was notoriously toxic, following the massive post-Katrina flooding. In the aftermath of Superstorm Sandy, the New York subway system (along with much of the rest of the city) flooded, prompting a massive exodus of rats into the streets.
With all these hazards staring us in the face, it would be (at best) irresponsible to ignore them. In the United States, our new reality is one in which historically-unprecedented weather events attack with increasing severity. It is a reality where our early/mid-20th Century infrastructure and mindset is utterly – completely, laughably – insufficient to cope with the punishments our planet is likely to mete out, now and in the future. Confronting the realities of global climate change means we must confront the shortcomings of local, national and global infrastructure.
