It’s spring and that means it’s time for nature’s critical pollinators to get busy. As you undoubtedly know, bee populations are in trouble and can use any kind of help they can get. Bees work hard this time of year and need available sources of water to rehydrate. They get this water from places like bird baths, rivers and streams, and open pools of water, but they risk drowning. You can help give them an easier place to safely drink by, as this post suggests, placing marbles inside of a shallow bath of water.
But as one guy points out in the comments on the linked page, the drawback to this design is that you have to maintain the water level (e.g. a heavy rain could drown your marbles). His bee watering hole is covered with a plastic mesh floating on wine corks. This way, regardless of the water level, the bees always have safe access to the reservoir beneath. Another variation I’ve seen is to float the bottom half of an egg carton on a pool of water. The carton will saturate but not sink, creating little islands for the bees to stand on while they refuel.
[Thanks to Susan Jamison for the link.]