# Paint splotches on sidewalk above sewer grates? **URL:** \ **Category:** Factual Questions\ **Created:** [August 19, 2010, 3:42am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707 "2010-08-19T03:42:04Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![srsny](https://avatars.discourse-cdn.com/v4/letter/s/22d042/32.png) [@srsny](https://boards.straightdope.com/u/srsny)\ **Post date:** [August 19, 2010, 3:42am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/1 "2010-08-19T03:42:04Z")
I’ve recently noticed that here in San Francisco that there are paint splotches on the sidewalks above many of the sewer grates in the city, at least those along my walk to work. Not just a single paint splotch, but layers of different color paint splotches, indicating that this event has taken place numerous times. This past week, I noticed that the pink paint splotch I had been looking at for the past month had been splotched over with white. It’s actually quite pretty, in an abstract sort of way. You can see a pic in an album on my Facebook page here: [http://www.facebook.com/album.php?aid=2075133&id=1437254136&l=642bc38930](http://www.facebook.com/album.php?aid=2075133&id=1437254136&l=642bc38930) So, anybody know what these things are? I’m thinking maybe an indication that some sort of frequent inspection has taken place? Thanks! ---
**Author:** ![Flutterby](https://avatars.discourse-cdn.com/v4/letter/f/6f9a4e/32.png) [@Flutterby](https://boards.straightdope.com/u/Flutterby)\ **Post date:** [August 19, 2010, 3:52am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/2 "2010-08-19T03:52:25Z")
I was going to suggest it’s faded fish\*, but from the picture it’s obviously not so I can’t help you. It does look interesting though. \*Groups paint fish next to the sewer drains, they’re supposed to be a reminder not to dump stuff down the drain. The program is called [Yellow Fish Road](http://www.yellowfishroad.org/) ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [August 19, 2010, 6:57am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/3 "2010-08-19T06:57:12Z")
It’s late and I’m feeling cranky, so I’m going to be a little less reticent about criticizing an OP with an honest question than usual: Caption your pictures. And link to ONE, not the entire page. Take the picture from far enough back that we can tell what we’re looking at. It’s obviously something done by a work crew, but without knowing its context, a dot is impossible to identify. OK, I have made a small concession to politeness, and halved the word count in the process. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [August 19, 2010, 7:57am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/4 "2010-08-19T07:57:07Z")
I’m guessing “art student project/prank”. A few years ago a bunch of students painted all the manhole covers in my city pink, just for the hell of it. This could be something similar. ---
**Author:** ![kferr](https://avatars.discourse-cdn.com/v4/letter/k/71e660/32.png) [@kferr](https://boards.straightdope.com/u/kferr)\ **Post date:** [August 19, 2010, 11:07am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/5 "2010-08-19T11:07:20Z")
I see similar in the UK and here it means that that drain has been cleaned or inspected. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 19, 2010, 1:54pm UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/6 "2010-08-19T13:54:43Z")
They periodically spray under manhole covers for roaches around here. I would suspect that they are doing something similar, and are just marking to let the inspectors know were they’ve sprayed / cleaned / inspected. ---
**Author:** ![cantara](https://avatars.discourse-cdn.com/v4/letter/c/6f9a4e/32.png) [@cantara](https://boards.straightdope.com/u/cantara)\ **Post date:** [August 19, 2010, 2:20pm UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/7 "2010-08-19T14:20:51Z")
In our community in Ontario they put a paint splotch on the sewer grate after they have treated that sewer with mosquito larvacides. > [@](#): > > [In catch basins](http://www.halton.ca/cms/One.aspx?portalId=8310&pageId=9911) - Methoprene is used. Methoprene is a synthetically produced mosquito hormone or growth regulator that interferes with the mosquito life cycle. It prevents the mosquito larva from reaching maturity and reproduction. Methoprene is used in catch basins if larvae are identified. This product is applied in a pellet or briquet form. > Catch basins collect water, dirt and other debris. Water in a catch basin rises to a certain level inside the basin, then drains into an outflow pipe, which is a storm sewer. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [August 19, 2010, 2:44pm UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/8 "2010-08-19T14:44:42Z")
[QUOTE=cantara] In our community in Ontario they put a paint splotch on the sewer grate after they have treated that sewer with mosquito larvacides. [/QUOTE] We have our winner. [The city has been using bike messengers for a few years to put insecticide in the storm drains](http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/08/17/BAGKTE8S2A1.DTL). The color splotches indicate broadly when it was last treated. They even have their own [website](http://mosquitosf.com/). [Hey bugs, here comes the yummies!](http://pestec.com/press.html) ---
**Author:** ![mnemosyne](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mnemosyne](https://boards.straightdope.com/u/mnemosyne)\ **Post date:** [August 20, 2010, 1:52am UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/9 "2010-08-20T01:52:53Z")
In general, spray paint splotches on roads, sidewalks and grates/manhole covers indicate either a mapping of sewer/cable/pipe lines and/or that some maintenance action has taken place at that location. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [August 20, 2010, 12:54pm UTC](https://boards.straightdope.com/t/paint-splotches-on-sidewalk-above-sewer-grates/550707/10 "2010-08-20T12:54:51Z")
[QUOTE=mnemosyne] In general, spray paint splotches on roads, sidewalks and grates/manhole covers indicate either a mapping of sewer/cable/pipe lines and/or that some maintenance action has taken place at that location. [/QUOTE] That’s a different endeavor. Markings to indicate underground utility locations are done with as much precision as one can muster from a can of spray paint, and there’s a whole “language” to them - red is always electric power, blue is always water, etc. They wouldn’t indicate pipes or wires with blotches to begin with - lines are marked out with painted lines in the direction of the underground service. I’d suspect that the bug busters are just using whatever color strikes their fancy.