Sign for stagnant/unmaintained swimming pools that have been treated by the Health Department to help prevent mosquitos:

The City of Richardson responds to complaints of stagnant swimming pools. The stagnant water in abandoned, unmaintained swimming pools typically contain algae/nutrients that female mosquitos value when choosing a site to lay eggs.

Health Department staff  treat stagnant swimming pools with larvicide to prevent mosquito eggs from developing into adults. The extended release larvicide we use is effective for up to 150 days and does not affect other species of wildlife.  These treated locations are identified with this sign posted nearby, most likely on the fence around the swimming pool.