MaunaluA Bay

Maunalua Bay is a treasured body of water, important for culture, livelihoods, and recreation.

The Maunalua Bay region stretches from Black Point (Kupikipikio) in the west to Portlock Point (Kawaihoa Point) in the east and to the summit of the Ko'olau Mountains. The region is approximately 28 mi2 in size and has eight miles of shoreline fronting the Bay. Maunalua Bay comprised about 6.5 mi2 of submerged waters. Ten watersheds feed into the Bay.

Over the last decades, the health of the Bay has declined due to a growing East O’ahu. One significant issue is how urban and storm water runoff flows directly into the Bay, untreated. The water that flows off roofs, over driveways and parking lots, and down streets into one of the region’s 5,000 storm drains brings sediment, garbage, pollutants and chemicals. Runoff threatens the biodiversity, natural resources, and the quality of life.

What's more, the extensive pavement means flooding for area residents is worse as less water is trapped or soaked up in the urban areas. 

The Hawai’i Department of Health declared Maunalua Bay an impaired water body, meaning that levels of parameters tested exceed the State limits. Other scientific studies and resident knowledge also point to a damaged system.

Today's nearshore reef flat is dominated by invasive alien algae, a significant shift from the once sandy bottom with abundant native limu, seagrass, and coral. It is the uncontrolled influx of sediment and pollutants that allows the invasive alien algae to thrive.

We can control what flows into the Bay. Each individual in this community can take actions that will collectively mitigate urban/stormwater runoff issues and create a healthy urban environment while providing environmental, social, cultural, and economic benefits.


 MS4 system

Any structure designed or used to collect or convey stormwater

Municipal Separate Stormwater System (MS4) include drain inlets, catch basins, pipes, gutters, channels, ditches, cemented road side swales, and culverts. These structures take the water and associated sediment and pollutants off land and into the Bay quickly and untreated.

With the exception of Wailupe Stream, all streams are cemented.


Impervious Cover

Any type of surface that doesn’t absorb rainfall

Surfaces such as stone, rooftops, patios, driveways, sidewalks, roadways, parking lots, and some decks are considered impervious cover.

Urban and stormwater runoff is exacerbated by the Maunalua Bay region's urban area due to it's impervious nature.


If the draining water doesn't evaporate or soak into the ground, excessive water may cause flooding, damage to homes and businesses, erode stream channels, and bay pollution.


Polluted Runoff

A major source of water pollution

As the water runs along a surface, it picks up litter, petroleum, chemicals, fertilizers, and other toxic substances.


Pollutants may include antifreeze, grease, oil, and heavy metals from cars; fertilizers, pesticides and other chemicals from gardens, homes and businesses; bacteria from pet wastes and failing septic systems; and sediment from poor construction site practices.

Many of these pollutants can cause problems in very small amounts and damage or destroy fish and wildlife habitat.

What is Green Infrastructure?

Green infrastructure is a system that helps to prevent runoff from urban development, and thereby minimizing the quantity of urban and stormwater and associated sediment, debris, and pollutants flowing our storm drain system.

How does it affect you?

Green infrastructure leads to many benefits:

Resilience from flooding

Improved water quality and ecosystem habitat

Reuse of water (lower water bills)

Growth of beautiful native landscapes

What can you do to help?

Join this campaign to learn how to install a rain garden or cistern for roof catchment, plant a tree, spread awareness, and more.