Long Island Surface Water

Science Center Objects

Streams either gain water from inflow of groundwater from the underlying aquifer or lose water by outflow to the underlying aquifer. Many streams do both, gaining in some reaches and losing in other reaches. Furthermore, the groundwater flow directions near any given stream can change seasonally as the altitude of the water table changes with respect to the stream-surface altitude or when rapid rises in stream stage during storms cause recharge to the streambank (known as “bank storage”). Under natural conditions, groundwater makes some contribution to streamflow in most physiographic and climatic settings.

Some of the larger and better known fresh surface-water bodies on Long Island are shown below. All bodies of fresh surface water shown on the map are perennial — that is, they contain water during the entire year. In addition, all the streams discharge to nearby salt water bodies.

In overall aspect, the present locations of Long Island's streams were determined mainly by the ancient drainage pattern that developed during the last ice age. Accordingly, most of the streams flow in broad, shallow valleys that were formed by the much larger streams which existed during melting of the ice sheet. All the southward-flowing streams have gentle gradients that, throughout most of their reaches, average about 10 feet per mile. The northward-flowing streams generally have steeper gradients that average about 20-40 feet per mile (Cohen and others, 1968).

Two distinctly different types of natural lakes and ponds are found on Long Island — water-table and perched lakes and ponds. Lake Ronkonkoma is a water-table lake, its bottom extending to a depth of about 60 feet below the water table. Lake Success is one of the better known examples of a perched lake on Long Island. Both of these lakes and many other natural lakes and ponds on Long Island, including Lake Panamoka, in Ridge, N.Y. are sometimes referred to as "kettle-hole" lakes. Such lakes fill depressions formed by blocks of ice that were buried during the last ice age and subsequently melted. Numerous artificial lakes and ponds have been built on Long Island. The larger ones were formed by the construction of low dams across streams. Hempstead and Belmont Lakes are well known examples of this type of lake (Cohen and others, 1968).

During the 19th and the early part of the 20th century, Long Island's streams, lakes, and ponds were used extensively as sources of water supply and for power to operate sawmills and gristmills. Presently, only insignificant quantities of surface water are used for water supply, and all the mills have been long since abandoned, except for several preserved as museums. The surface-water bodies of Long Island are, however, used extensively for recreation.

Location of the streams and selected gaging stations are shown in figure 10:

 Map of streams and gaging locations on Long Island, New York
Figure 10. Streams and gaging locations on Long Island, New York(Public domain.)

Winter and others (1998) provides a thorough description of the interaction of groundwater and streams, lakes and wetlands (figures 11A and 11B). On Long Island streams gain water from inflow of groundwater through the streambed.

graph of gaining streams and water-table contour map
Gaining streams receive water from the groundwater system as shown in (A) and can be determined from water-table contour maps because the contour lines point in the upstream direction where they cross the stream as shown in (B) (Winter and others, 1998).(Public domain.)


Table of Contents

State of the Aquifer, Long Island, New York - Introduction

Location and Physical Setting


  1. Hydrolgeologic Units
  2. Fresh and Saltwater Relations/Interactions

State of the Aquifer System

  1. Precipitation
  2. NWIS - the USGS Data Archive 
  3. Surface Water - Streamflow
  4. Groundwater Levels
  5. Water Table and Surface Maps
  6. Water Use
  7. Groundwater Budget
  8. Inflow to the Groundwater System
  9. Outflow from the Groundwater System
  1. Case Studies

Interactive Content