Firstly, using lakes to cool power plants is not unusual or uncommon. They don't really make that clear, and it feels like they want the reader to think this is nefarious. To me the title of this should be something more like "Residents forgot the lake gets warmer when the power plant operates".
As far as the 135 million allowed to be discharged into the lake daily, it is an incredibly small amount compared to the size of the lake. According to Wikipedia, the volume of the lake is 3.81 cu/miles of water. A quick search tells me 1 cu/mi =~ 1.1 trillion gallons. Okay, some more rough math gives us a total of about 4.2 trillion gallons in the lake of which 135M gallons is something like 0.000032% of the total volume.
So my point is that when the article throws a figure like 135M gallons at you with no context it seems huge. But when you look at it in context, 3 one hundred thousands of one percent of the total, I have a hard time imagining that has any measurable impact on the lake whatsoever. I'm sure the quoted resident that lives very near to the plant had noticed the warmth, but anywhere else on the lake?
On top of this, the plant is under strict scrutiny by the regulators, and they appear to be operating withing the limits outlined by said regulators. So if there is anyone to get mad at here it's not the plant operators, it's the Department of Environmental Conservation.