The Lincoln Memorial Reflecting Pool was supposed to be the centerpiece of President Trump’s makeover of Washington. His administration spent $16.4 million on its renovation, giving out no-bid contracts to improve its filtration system and to spread blue waterproof coating across its large concrete floor.

But just days after the pool was largely refilled with water on June 5, problems appeared. The water turned bright green. The new blue coating peeled and floated to the surface.

In recent days, Mr. Trump has repeatedly blamed these problems on vandals and said six people had been arrested. But his administration has provided little evidence to back up some of his claims, and it appears no charges have been filed yet in court. Experts say other factors could have caused the major issues that have plagued the pool.

Here’s what to know.

What’s gone wrong with the Reflecting Pool?

At least three problems have surfaced since the pool was refilled.

The most visible one was algae, which has plagued the pool for decades. Days after the pool was refilled, algae returned and turned the water a bright shade of green. (That problem now seems to have abated: The water appears clearer, with new purification systems and Park Service employees vacuuming up algae).

As the algae bloomed, another problem became apparent. Sections of the pool’s new blue coating began to peel off the bottom and float up to the surface.