Water is a funny thing. In ponds and lakes fifteen feet deep or more, the water will set up in layers, or strata, depending on density and temperature.
Most of the time, this stratification will result in cold, manky water at the bottom of the column and warmer water at the top, separated at a sharply-defined layer called a thermocline.
Now, I call the cold bottom water "manky" because that is where the dead stuff winds up. Which is kind of logical because -- as we know -- gravity always wins in the end and it drags the leaves, branches, dead turtles, deceased fish, corpsified snakes, and various and sundry wastes (hey, you think fish climb out of the lake to go to the litter box?) all wind up in the cold bottom water.
Now, Mama Nature has to get rid of all the above, so we've got decomposition down at the bottom, with the attendant bacteria, sulphides, sulphites, methanes and all the other olfactory goodness that goes along with that sort of thing -- and we've got a thermocline capping it all off which means that the top, oxygen-rich water, and the bottom, oxygen-poor water never mix, and the bottom water stays at the bottom.
Except during the fall, when changing temperatures alter the density of water, and occasionally in the spring for the same reason -- this regular event is called the lake "turnover" or inversion.
Sometimes, though, you can get an inversion or turnover triggered by large amounts of rainfall.
Like right now.
So. We're getting extraordinary amounts of rainfall, which all pounds into the lakes, we've got rivers and creeks and arroyos all jetting rainwater into the lakes -- and the thermocline tears apart, no longer keeping top water and bottom water separate, and the two mix or "turnover".
All those sulphides, sulphites and methane hit the top of the water and outgas, and all that bacteria hits the oxygen-rich, nutrient-rich surface water and promptly throw a single-cell orgy --
-- and my glass of water drawn from the faucet (and out of the convenience store fountain) tastes like it's straight out of a swamp.
Which -- come to think -- is a pretty accurate description of what the city lake resembles right now.
Bottled water for a couple of weeks, I guess.