https://www.gamespot.com/articles/new-pokemon-go-field-research-tasks-available-now-/1100-6462186/

A new month is now underway, and developer Niantic has rolled out a new batch of Field Research tasks in Pokemon Go. This month's missions are themed around Water-types, and if you manage to complete enough of them, you'll earn another opportunity to catch the Legendary Aurora Pokemon, Suicune.

Suicune is one of the three Legendary dogs first introduced in Pokemon Gold and Silver, alongside Raikou and Entei--both of which were featured in August and September's Field Research tasks, respectively. In order to encounter Suicune, you'll first need to achieve a Research Breakthrough. This is done by collecting seven stamps, one of which is doled out each day you complete a Field Research task.