Colonies are generally white in color, though they may turn grey under the presence of bacteria or other debris which has become caught in the fibrous mass.

This second zoospore has a longer cycle during which most dispersal happens; it will continue to encyst and release a new spore in a process called polyplanetism until it finds a suitable substrate.

When a suitable medium is located, the hairs surrounding the spore will lock onto the substrate so that the sexual reproduction phase can start.

It is also during this stage of polyplanetism that the Saprolegnia are capable of causing infection; the most pathogenic species have tiny hooks at the end of their hairs to enhance their infectious ability.

The extensive mortalities of salmon and migratory trout in the rivers of western Europe in the 1970s and 1980s in the UDN outbreak were probably almost all ultimately caused by the secondary Saprolegnia infections.